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@inproceedings{BonsangueEtAl14,
  author = {Bonsangue, M. and
               Rot, J. and
               Ancona, D. and
               de Boer, F.S. and
               Rutten, J.},
  editor = {Esparza, J. and
               Fraigniaud, P. and
               Husfeldt, T. and
               Koutsoupias, E.},
  title = {A Coalgebraic Foundation for Coinductive Union Types},
  booktitle = {{Automata, Languages, and Programming - 41st International
               Colloquium, ICALP 2014, Copenhagen, Denmark, July 8-11,
               2014, Proceedings, Part II}},
  publisher = {Springer},
  series = {{Lecture Notes in Computer Science}},
  volume = {8573},
  year = {2014},
  pages = {62-73},
  keywords = {{coinduction}},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/BonsangueEtAl14.pdf},
  abstract = {{This paper introduces a coalgebraic foundation for coinductive types, interpreted as sets of values and extended
with set theoretic union. We give a sound and complete characterization of semantic subtyping in terms of
inclusion of maximal traces. Further, we provide a technique for reducing subtyping to inclusion between sets of
finite traces, based on approximation. We obtain inclusion of tree languages as a sound and complete
method to show semantic subtyping of recursive types with basic types, product and union, interpreted coinductively.
}}
}
@article{AnconaDovier13,
  keywords = {{coinduction}},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/AnconaDovier14.pdf},
  author = {Ancona, D. and Dovier, A.},
  title = {{co-LP: Back to the Roots}},
  journal = {{Theory and Practice of Logic Programming }},
  volume = {13},
  number = {4-5-Online-Supplement},
  year = {2013},
  abstract = {Recently, several papers dealing with co-inductive logic
programming have been proposed, dealing with pure Prolog and
constraint logic programming, with and without negation.
In this paper we revisit and use, as much as possible,
some fundamental results developed in the Eighties
to analyze the foundations,
and  to clarify the possibilities but also
the intrinsic theoretical limits of this programming paradigm.
}
}
@inproceedings{AnconaCorradi14,
  booktitle = {{ECOOP 2014 - Object-Oriented Programming}},
  keywords = {{objects,types,coinduction}},
  note = {{To appear}},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/CompleteCoinductiveSubtyping.pdf},
  author = {Ancona, D. and Corradi, A.},
  title = {{Sound and complete subtyping between coinductive types for object-oriented languages}},
  year = {2014},
  abstract = {Structural subtyping is an important notion for effective static type analysis;
it can be defined either axiomatically by a collection of subtyping rules, or by means of set inclusion between type interpretations, following
the semantic subtyping approach, which is more intuitive, and allows simpler proofs of the expected properties of the subtyping relation.  

In object-oriented programming, recursive types typically correspond to inductively defined data structures, and subtyping is defined axiomatically; 
however, in object-oriented languages objects can also be cyclic, but inductive types
cannot represent them as precisely as happens for coinductive types. 

We study semantic subtyping between coinductive types with records and unions, which are particularly interesting for object-oriented programming, 
show cases where it allows more precise type analysis, and develop a sound and complete effective algorithm for deciding it.
To our knowledge, this is the first proposal for a sound and complete algorithm for semantic subtyping between coinductive types.
}
}
@article{AnconaCOMLAN13,
  institution = {{DIBRIS - Universit{\`{a}} di Genova}},
  keywords = {{coinduction,corecursion}},
  note = {{Extended version of \url{http://www.disi.unige.it/person/AnconaD/papers/Conferences_abstracts.html#AnconaSAC12}{SAC 2012}}},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/COMLAN13.pdf},
  author = {Ancona, D.},
  title = {{Regular corecursion in Prolog}},
  journal = {{Computer Languages, Systems \& Structures}},
  volume = {39},
  number = {4},
  pages = {142-162},
  year = {2013},
  abstract = {Corecursion is the ability of defining a function that
                   produces some infinite data in terms of the function
                   and the data itself, as supported by lazy evaluation.
                   However, in languages such as Haskell strict operations
                   fail to terminate even on infinite regular data, that
                   is, cyclic data. Regular corecursion is naturally
                   supported by coinductive Prolog, an extension where
                   predicates can be interpreted either inductively or
                   coinductively, that has proved to be useful for formal
                   verification, static analysis and symbolic evaluation
                   of programs. In this paper we use the meta-programming
                   facilities offered by Prolog to propose extensions to
                   coinductive Prolog aiming to make regular corecursion
                   more expressive and easier to program with. First, we
                   propose a new interpreter to solve the problem of
                   non-terminating failure as experienced with the
                   standard semantics of coinduction (as supported, for
                   instance, in SWI-Prolog). Another problem with the
                   standard semantics is that predicates expressed in
                   terms of existential quantification over a regular term
                   cannot directly defined by coinduction; to this aim, we
                   introduce finally clauses, to allow more flexibility in
                   coinductive definitions. Then we investigate the
                   possibility of annotating arguments of coinductive
                   predicates, to restrict coinductive definitions to a
                   subset of the arguments; this allows more efficient
                   definitions, and further enhance the expressive power
                   of coinductive Prolog. We investigate the effectiveness
                   of such features by showing different example programs
                   manipulating several kinds of cyclic values, ranging
                   from automata and context free grammars to graphs and
                   repeating decimals; the examples show how computations
                   on cyclic values can be expressed with concise and
                   relatively simple programs. The semantics defined by
                   these vanilla meta-interpreters are an interesting
                   starting point for a more mature design and
                   implementation of coinductive Prolog. }
}
@inproceedings{AZ_FTfJP13,
  booktitle = {{Formal techniques for Java-like programs (FTfJP13)}},
  keywords = {{objects, coinduction, corecursion}},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/AZ-FTfJP13.pdf},
  author = {Ancona, D. and Zucca, E.},
  title = {{Safe Corecursion in coFJ}},
  pages = {2:1--2:7},
  year = {2013},
  abstract = {In previous work we have presented coFJ, an extension
                   to Featherweight Java that promotes coinductive
                   programming, a sub-paradigm expressly devised to ease
                   high-level programming and reasoning with cyclic data
                   structures. The coFJ language supports cyclic objects
                   and regularly corecursive methods, that is, methods
                   whose invocation terminates not only when the
                   corresponding call trace is finite (as happens with
                   ordinary recursion), but also when such a trace is
                   infinite but cyclic, that is, can be specified by a
                   regular term, or, equivalently, by a finite set of
                   recursive syntactic equations. In coFJ it is not easy
                   to ensure that the invocation of a corecursive method
                   will return a well-defined value, since the recursive
                   equations corresponding to the regular trace of the
                   recursive calls may not admit a (unique) solution; in
                   such cases we say that the value returned by the method
                   call is undetermined. In this paper we propose two new
                   contributions. First, we design a simpler construct for
                   defining corecursive methods and, correspondingly,
                   provide a more intuitive operational semantics. For
                   this coFJ variant, we are able to define a type system
                   that allows the user to specify that certain
                   corecursive methods cannot return an undetermined
                   value; in this way, it is possible to prevent unsafe
                   use of such a value. The operational semantics and the
                   type system of coFJ are fully formalized, and the
                   soundness of the type system is proved. }
}
@inproceedings{Ancona_FTfJP14,
  booktitle = {{Formal techniques for Java-like programs (FTfJP14)}},
  keywords = {{semantics, types, objects, coinduction}},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/Ancona-FTfJP14.pdf},
  author = {Ancona, D.},
  title = {{How to Prove Type Soundness of Java-like Languages Without Forgoing Big-step Semantics}},
  pages = {1:1--1:6},
  year = {2014},
  articleno = {1},
  publisher = {ACM},
  abstract = {Small-step operational semantics is the most commonly employed formalism for
proving type soundness of statically typed programming languages, because 
of its ability to distinguish stuck from non-terminating computations,
as opposed to big-step operational semantics.

Despite this, big-step operational semantics is more abstract, and more
useful for specifying interpreters. 

In previous work we have proposed a new proof technique to prove type soundness
of a Java-like language expressed in terms of its big-step operational semantics.
However the presented proof is rather involved, since it
requires showing that the set of proof trees defining the semantic judgment forms a complete metric space
when equipped with a specific distance function.
  
In this paper we propose a more direct and abstract approach that exploits a standard and general compactness property
of the metric space of values, that allows approximation of the coinductive big-step semantics in terms of the small-step one;
in this way type soundness can be proved by standard mathematical induction.
}
}
@inproceedings{AnconaSAC12,
  author = {Ancona, D.},
  title = {Regular corecursion in {P}rolog},
  booktitle = {A{CM} {S}ymposium on {A}pplied {C}omputing ({SAC}
                   2012)},
  editor = {Ossowski, S. and Lecca, P.},
  pages = {1897--1902},
  abstract = {Co-recursion is the ability of defining a function
                   that produces some infinite data in terms of the
                   function and the data itself, and is typically
                   supported by languages with lazy evaluation. However,
                   in languages as Haskell strict operations fail to
                   terminate even on infinite regular data. Regular
                   co-recursion is naturally supported by co-inductive
                   Prolog, an extension where predicates can be
                   interpreted either inductively or co-inductively, that
                   has proved to be useful for formal verification, static
                   analysis and symbolic evaluation of programs. In this
                   paper we propose two main alternative vanilla
                   meta-interpreters to support regular co-recursion in
                   Prolog as an interesting programming style in its own
                   right, able to elegantly solve problems that would
                   require more complex code if conventional recursion
                   were used. In particular, the second meta-interpreters
                   avoids non termination in several cases, by restricting
                   the set of possible answers. The semantics defined by
                   these vanilla meta-interpreters are an interesting
                   starting point to study new semantics able to support
                   regular co-recursion for non logical languages. },
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/AnconaSAC12.pdf},
  keywords = {coinduction,corecursion},
  year = 2012
}
@inproceedings{AnconaECOOP12,
  author = {Ancona, D.},
  title = {Soundness of {O}bject-{O}riented {L}anguages with
                   {C}oinductive {B}ig-{S}tep {S}emantics},
  booktitle = {E{COOP} 2012 - {O}bject-{O}riented {P}rogramming},
  editor = {Noble, J.},
  volume = {7313},
  pages = {459--483},
  publisher = {Springer},
  abstract = {It is well known that big-step operational semantics
                   are not suitable for proving soundness of type systems,
                   because of their inability to distinguish stuck from
                   non-terminating computations. We show how this problem
                   can be solved by interpreting coinductively the rules
                   for the standard big-step operational semantics of a
                   Java-like language, thus making the claim of soundness
                   more intuitive: whenever a program is well-typed, its
                   coinductive operational semantics returns a value.
                   Indeed, coinduction allows non-terminating computations
                   to return values; this is proved by showing that the
                   set of proof trees defining the semantic judgment forms
                   a complete metric space when equipped with a proper
                   distance function. In this way, we are able to prove
                   soundness of a nominal type system w.r.t. the
                   coinductive semantics. Since the coinductive semantics
                   is sound w.r.t. the usual small-step operational
                   semantics, the standard claim of soundness can be
                   easily deduced. },
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/AnconaECOOP12.pdf},
  keywords = {semantics, types, objects, coinduction},
  year = 2012
}
@inproceedings{AL-TCS12,
  author = {Ancona, D. and Lagorio, G.},
  title = {Static single information form for abstract
                   compilation},
  booktitle = {Theoretical {C}omputer {S}cience ({IFIP} {TCS} 2012)},
  editor = {Baeten, J. C.M. and Ball, T. and de Boer, F. S.},
  volume = {7604},
  series = {Lecture Notes in Computer Science},
  pages = {10--27},
  publisher = {Springer},
  abstract = {In previous work we have shown that more precise type
                   analysis can be achieved by exploiting union types and
                   static single assignment (SSA) intermediate
                   representation (IR) of code. In this paper we exploit
                   static single information (SSI), an extension of SSA
                   proposed in literature and adopted by some compilers,
                   to allow assignments of more precise types to variables
                   in conditional branches. In particular, SSI can be
                   exploited rather easily and effectively to infer more
                   precise types in dynamic object-oriented languages,
                   where explicit runtime typechecking is frequently used.
                   We show how the use of SSI form can be smoothly
                   integrated with abstract compilation, our approach to
                   static type analysis. In particular, we define abstract
                   compilation based on union and nominal types for a
                   simple dynamic object-oriented language in SSI form
                   with a runtime typechecking operator, to show how
                   precise type inference can be.},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/AL-TCS12.pdf},
  keywords = {objects,types,coinduction},
  year = 2012
}
@inproceedings{AZ-CoLP12,
  author = {Ancona, D. and Zucca, E.},
  title = {Translating Corecursive {F}eatherweight {J}ava in
                   Coinductive Logic Programming},
  booktitle = {{Co-LP} 2012 - A workshop on {C}oinductive {L}ogic
                   {P}rogramming},
  abstract = {Corecursive FeatherWeight Java (coFJ) is a recently
                   proposed extension of the calculus FeatherWeight Java
                   (FJ), supporting cyclic objects and regular recursion,
                   and explicitly designed to promote a novel programming
                   paradigm inspired by coinductive Logic Programming
                   (coLP), based on coinductive, rather than inductive,
                   interpretation of recursive function definitions. We
                   present a slightly modified version of coFJ where the
                   application of a coinductive hypothesis can trigger the
                   evaluation of a specific expression at declaration,
                   rather than at use site. Following an approach inspired
                   by abstract compilation, we then show how coFJ can be
                   directly translated into coLP, when coinductive SLD is
                   extended with a similar feature for explicitly solving
                   a goal when a coinductive hypothesis is applied. Such a
                   translation is quite compact and, besides showing the
                   direct relation between coFJ and coinductive Prolog,
                   provides a first prototypical but simple and effective
                   implementation of coFJ.},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/AZ-CoLP12.pdf},
  keywords = {objects, coinduction, corecursion},
  year = 2012
}
@inproceedings{AZ-FTfJP12,
  author = {Ancona, D. and Zucca, E.},
  title = {Corecursive {F}eatherweight {J}ava},
  booktitle = {Formal techniques for {J}ava-like programs
                   ({FT}f{JP}12)},
  abstract = {Despite cyclic data structures occur often in many
                   application domains, object-oriented programming
                   languages provide poor abstraction mechanisms for
                   dealing with cyclic objects. Such a deficiency is
                   reflected also in the research on theoretical
                   foundation of object-oriented languages; for instance,
                   Featherweigh Java (FJ), which is one of the most
                   widespread object-oriented calculi, does not allow
                   creation and manipulation of cyclic objects. We propose
                   an extension to Featherweight Java, called coFJ, where
                   it is possible to define cyclic objects, \{abstractly
                   corresponding to regular terms\}, and where an
                   abstraction mechanism, called regular corecursion, is
                   provided for supporting implementation of coinductive
                   operations on cyclic objects. We formally define the
                   operational semantics of coFJ, and provide a handful of
                   examples showing the expressive power of regular
                   corecursion; such a mechanism promotes a novel
                   programming style particularly well-suited for
                   implementing cyclic data structures, and for supporting
                   coinductive reasoning. },
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/AZ-FTfJP12.pdf},
  keywords = {objects, coinduction, corecursion},
  year = 2012
}
@inproceedings{ACLD10-FoVeOOS10,
  author = {Ancona, D. and Corradi, A. and Lagorio, G. and
                   Damiani, F.},
  title = {Abstract compilation of object-oriented languages into
                   coinductive {CLP}({X}): can type inference meet
                   verification?},
  booktitle = {Formal {V}erification of {O}bject-{O}riented
                   {S}oftware {I}nternational {C}onference, {F}o{V}e{OOS}
                   2010, {P}aris, {F}rance, {J}une 28-30, 2010,
                   \textbf{{R}evised {S}elected {P}apers}},
  editor = {Beckert, B. and March\'e, C.},
  volume = {6528},
  series = {Lecture Notes in Computer Science},
  publisher = {Springer Verlag},
  abstract = {This paper further investigates the potential and
                   practical applicability of abstract compilation in two
                   different directions. First, we formally define an
                   abstract compilation scheme for precise prediction of
                   uncaught exceptions for a simple Java-like language;
                   besides the usual user declared checked exceptions, the
                   analysis covers the runtime ClassCastException. Second,
                   we present a general implementation schema for abstract
                   compilation based on coinductive CLP with variance
                   annotation of user-defined predicates, and propose an
                   implementation based on a Prolog prototype
                   meta-interpreter, parametric in the solver for the
                   subtyping constraints.},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/ACLD10-FoVeOOS10.pdf},
  keywords = {objects,types,coinduction},
  year = 2011
}
@article{AL-RAIRO11,
  author = {D. Ancona and G. Lagorio},
  title = {Idealized coinductive type systems for imperative
                   object-oriented programs},
  journal = {RAIRO - Theoretical Informatics and Applications},
  volume = {45},
  number = {1},
  pages = {3-33},
  abstract = {In recent work we have proposed a novel approach to
                   define idealized type systems for object-oriented
                   languages, based on abstract compilation of programs
                   into Horn formulas which are interpreted w.r.t. the
                   coinductive (that is, the greatest) Herbrand model. In
                   this paper we investigate how this approach can be
                   applied also in the presence of imperative features.
                   This is made possible by con- sidering a natural
                   translation of Static Single Assignment intermediate
                   form programs into Horn formulas, where phi functions
                   correspond to union types.},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/RAIRO.pdf},
  keywords = {objects,types,coinduction},
  url = {http://www.rairo-ita.org},
  year = 2011
}
@inproceedings{AnconaFTfJP11,
  author = {Ancona, D.},
  title = {Coinductive big-step operational semantics for type
                   soundness of {J}ava-like languages},
  booktitle = {Formal {T}echniques for {J}ava-like {P}rograms
                   ({FT}f{JP}11)},
  pages = {5:1--5:6},
  publisher = {ACM},
  abstract = {We define a coinductive semantics for a simple
                   Java-like language by simply interpreting coinductively
                   the rules of a standard big-step operational semantics.
                   We prove that such a semantics is sound w.r.t. the
                   usual small-step operational semantics, and then prove
                   soundness of a conventional nominal type system w.r.t.
                   the coinductive semantics. From these two results,
                   soundness of the type system w.r.t. the small-step
                   semantics can be easily deduced. This new proposed
                   approach not only opens up new possibilities for
                   proving type soundness, but also provides useful
                   insights on the connection between coinductive big-step
                   operational semantics and type systems.},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/FTfJP11.pdf},
  isbn = {978-1-4503-0893-9},
  keywords = {semantics, types, objects, coinduction},
  year = 2011
}
@techreport{AL-10-11,
  author = {Ancona, D. and Lagorio, G.},
  title = {On sound and complete axiomatization of coinductive
                   subtyping for object-oriented languages},
  institution = {DISI},
  note = {Submitted for journal publication. Extended version of
                   \url{http://www.disi.unige.it/person/AnconaD/papers/Conferences_abstracts.html#AL-FTfJP10}{FTfJP10}},
  abstract = {Coinductive abstract compilation is a novel technique,
                   which has been recently introduced for defining precise
                   type systems for object- oriented languages. In this
                   approach, type inference consists in translating the
                   program to be analyzed into a Horn formula f, and in
                   resolving a certain goal w.r.t. the coinductive (that
                   is, the greatest) Herbrand model of f. Type systems
                   defined in this way are idealized, since types and,
                   con- sequently, goal derivations, are not finitely
                   representable. Hence, sound implementable
                   approximations have to rely on the notions of regular
                   types and derivations, and of subtyping and subsumption
                   between types and atoms, respectively. In this paper we
                   address the problem of defining a sound and complete
                   axiomatization of a subtyping relation between
                   coinductive object and union types, defined as set
                   inclusion between type interpretations. Besides being
                   an important theoretical result, completeness is useful
                   for reasoning about possible implementations of the
                   subtyping relation, when restricted to regular types.},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/AL10-11.pdf},
  keywords = {objects,types,coinduction},
  month = nov,
  year = 2010
}
@techreport{ACLD10-08-ext,
  author = {Ancona, D. and Corradi, A. and Lagorio, G. and
                   Damiani, F.},
  title = {Abstract compilation of object-oriented languages into
                   coinductive {CLP}({X}): can type inference meet
                   verification? (extended version)},
  institution = {DISI},
  note = {Extended version of \url{http://www.disi.unige.it/person/AnconaD/papers/Conferences_abstracts.html#ACLD10-FoVeOOS10}{FoVeOOS10}},
  abstract = {This paper further investigates the potential and
                   practical applicability of abstract compilation in two
                   different directions. First, we formally define an
                   abstract compilation scheme for precise prediction of
                   uncaught exceptions for a simple Java-like language;
                   besides the usual user declared checked exceptions, the
                   analysis covers the runtime ClassCastException. Second,
                   we present a general implementation schema for abstract
                   compilation based on coinductive CLP with variance
                   annotation of user-defined predicates, and propose an
                   implementation based on a Prolog prototype
                   meta-interpreter, parametric in the solver for the
                   subtyping constraints. },
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/ACLD10ext.pdf},
  keywords = {objects,types,coinduction},
  month = aug,
  year = 2010
}
@inproceedings{AL-FTfJP10,
  author = {D. Ancona and G. Lagorio},
  title = {Complete coinductive subtyping for abstract
                   compilation of object-oriented languages},
  booktitle = {F{TFJP} '10: {P}roceedings of the 12th {W}orkshop on
                   {F}ormal {T}echniques for {J}ava-{L}ike {P}rograms},
  series = {ACM Digital Library},
  pages = {1:1--1:7},
  publisher = {ACM},
  abstract = {Coinductive abstract compilation is a novel technique,
                   which has been recently introduced, for defining
                   precise type systems for object-oriented languages. In
                   this approach, type inference consists in translating
                   the program to be analyzed into a Horn formula f, and
                   in resolving a certain goal w.r.t. the coinductive
                   (that is, the greatest) Herbrand model of f. Type
                   systems defined in this way are idealized, since types
                   and, consequently, goal derivations, are not finitely
                   representable. Hence, sound implementable
                   approximations have to rely on the notions of regular
                   types and derivations, and of subtyping and subsumption
                   between types and atoms, respectively. In this paper we
                   address the problem of defining a complete subtyping
                   relation <= between types built on object and union
                   type constructors: we interpret types as sets of
                   values, and investigate on a definition of subtyping
                   such that t\_1 <= t\_2 is derivable whenever the
                   interpretation of t\_1 is contained in the
                   interpretation of t\_2. Besides being an important
                   theoretical result, completeness is useful for
                   reasoning about possible implementations of the
                   subtyping relation, when restricted to regular types. },
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/FTfJP10.pdf},
  keywords = {objects,types,coinduction},
  url = {http://portal.acm.org/citation.cfm?id=1924520},
  year = 2010
}
@inproceedings{AL10-GandALF10,
  author = {D. Ancona and G. Lagorio},
  title = {Coinductive subtyping for abstract compilation of
                   object-oriented languages into {H}orn formulas},
  booktitle = {Proceedings of {G}and{ALF} 2010},
  editor = {{Montanari A.} and {Napoli M.} and {Parente M.}},
  volume = {25},
  series = {Electronic Proceedings in Theoretical Computer Science},
  pages = {214--223},
  abstract = {In recent work we have shown how it is possible to
                   define very precise type systems for object-oriented
                   languages by abstractly compiling a program into a Horn
                   formula f. Then type inference amounts to resolving a
                   certain goal w.r.t. the coinductive (that is, the
                   greatest) Herbrand model of f. Type systems defined in
                   this way are idealized, since in the most interesting
                   instantiations both the terms of the coinductive
                   Herbrand universe and goal derivations cannot be
                   finitely represented. However, sound and quite
                   expressive approximations can be implemented by
                   considering only regular terms and derivations. In
                   doing so, it is essential to introduce a proper
                   subtyping relation formalizing the notion of
                   approximation between types. In this paper we study a
                   subtyping relation on coinductive terms built on union
                   and object type constructors. We define an
                   interpretation of types as set of values induced by a
                   quite intuitive relation of membership of values to
                   types, and prove that the definition of subtyping is
                   sound w.r.t. subset inclusion between type
                   interpretations. The proof of soundness has allowed us
                   to simplify the notion of contractive derivation and to
                   discover that the previously given definition of
                   subtyping did not cover all possible representations of
                   the empty type. },
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/GandALF10.pdf},
  keywords = {objects,types,coinduction},
  year = 2010
}
@techreport{AnconaEtAl10,
  author = {Ancona, D. and Corradi, A. and Lagorio, G. and
                   Damiani, F.},
  title = {Abstract compilation of object-oriented languages into
                   coinductive {CLP}({X}): when type inference meets
                   verification},
  institution = {Karlsruhe Institute of Technology},
  note = {Formal {V}erification of {O}bject-{O}riented
                   {S}oftware. {P}apers presented at the {I}nternational
                   {C}onference, {J}une 28-30, 2010, {P}aris, {F}rance},
  abstract = {We propose a novel general approach for defining
                   expressive type systems for object-oriented languages,
                   based on abstract compilation of programs into
                   coinductive constraint logic programs defined on a
                   specific constraint domain X called type domain. In
                   this way, type checking and type inference amount to
                   resolving a certain goal w.r.t. the coinductive (that
                   is, the greatest) Herbrand model of a logic program
                   (that is, a Horn formula) with constraints over a fixed
                   type domain X. In particular, we show an interesting
                   instantiation where the constraint predicates of X are
                   syntactic equality and subtyping over coinductive
                   object and union types. The corresponding type system
                   is so expressive to allow verification of simple
                   properties like data structure invariants. Finally, we
                   show a prototype implementation, written in Prolog, of
                   the inference engine for coinductive CLP(X), which is
                   parametric in the solver for the type domain X.},
  booktitle = {Formal {V}erification of {O}bject-{O}riented
                   {S}oftware. {P}apers presented at the {I}nternational
                   {C}onference, {J}une 28-30, 2010, {P}aris, {F}rance},
  editor = {Beckert, B. and March\'e, C.},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/FOVEOOS10-preproc.pdf},
  keywords = {objects,types,coinduction},
  publisher = {Karlsruhe},
  series = {Karlsruhe Reports in Informatics (fr\"uher: Interner
                   Bericht. Fakult\"at f\"ur Informatik, Karlsruher
                   Institut f\"ur Technologie) ; 2010,13},
  year = 2010
}
@inproceedings{ALZ-TYPES08,
  author = {Ancona, D. and Lagorio, G. and Zucca, E.},
  title = {Type inference by coinductive logic programming},
  booktitle = {Post-{P}roceedings of {TYPES} 2008},
  editor = {Berardi S., Damiani F., de' Liguoro U.},
  volume = {5497},
  series = {Lecture Notes in Computer Science},
  publisher = {Springer Verlag},
  abstract = {We propose a novel approach to constraint-based type
                   inference based on coinductive logic programming. That
                   is, constraint generation corresponds to translation
                   into a conjunction of Horn clauses P, and constraint
                   satisfaction is defined in terms of the maximal
                   coinductive Herbrand model of P. We illustrate the
                   approach by formally defining this translation for a
                   small object-oriented language similar to Featherweight
                   Java, where type annotations in field and method
                   declarations can be omitted. In this way, we obtain a
                   very precise type inference and provide new insights
                   into the challenging problem of type inference for
                   object-oriented programs. Since the approach is
                   deliberately declarative, we define in fact a formal
                   specification for a general class of algorithms, which
                   can be a useful road maps to researchers. Moreover,
                   despite we consider here a particular language, the
                   methodology could be used in general for providing
                   abstract specifications of type inference for different
                   kinds of programming languages.},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/ALZ0908.pdf},
  keywords = {objects,types,coinduction},
  year = 2009
}
@inproceedings{AL-ECOOP09,
  author = {Ancona, D. and Lagorio, G.},
  title = {Coinductive type systems for object-oriented languages},
  booktitle = {ECOOP 2009 - Object-Oriented Programming},
  editor = {{S. Drossopoulou}},
  volume = {5653},
  series = {Lecture Notes in Computer Science},
  pages = {2--26},
  publisher = {Springer Verlag},
  note = {\textbf{Best paper prize}},
  abstract = {We propose a novel approach based on coinductive logic
                   to specify type systems of programming languages. The
                   approach consists in encoding programs in Horn formulas
                   which are interpreted w.r.t. their coinductive Herbrand
                   model. We illustrate the approach by first specifying a
                   standard type system for a small object-oriented
                   language similar to Featherweight Java. Then we define
                   an idealized type system for a variant of the language
                   where type annotations can be omitted. The type system
                   involves infinite terms and proof trees not
                   representable in a finite way, thus providing a
                   theoretical limit to type inference of object-oriented
                   programs, since only sound approximations of the system
                   can be implemented. Approximation is naturally captured
                   by the notions of subtyping and subsumption; indeed,
                   rather than increasing the expressive power of the
                   system, as it usually happens, here subtyping is needed
                   for approximating infinite non regular types and proof
                   trees with regular ones. },
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/ECOOP09.pdf},
  keywords = {objects,types,coinduction},
  year = 2009
}
@techreport{ALZ0708,
  author = {Ancona, D. and Lagorio, G. and Zucca, E.},
  title = {Type inference for {J}ava-like programs by coinductive
                   logic programming},
  institution = {DISI - Univ. of Genova},
  abstract = {Although coinductive logic programming (Co-LP) has
                   proved to have several applications, including
                   verification of infinitary properties, model checking
                   and bisimilarity proofs, type inference via Co-LP has
                   not been properly investigated yet. In this paper we
                   show a novel approach to solve the problem of type
                   inference in the context of Java-like languages, that
                   is, object-oriented languages based on nominal
                   subtyping. The proposed approach follows a generic
                   scheme: first, the program P to be analyzed is
                   translated into an approximating logic program P' and a
                   goal G; then, the solution of the type inference
                   problem corresponds to find an instantiation of the
                   goal G which belongs to the greatest model of P', that
                   is, the coinductive model of P'. Operationally, this
                   corresponds to find a co-SLD derivation of G in P',
                   according to the operational semantics of Co-LP
                   recently defined by Simon et al. [ICLP06,ICALP07]. A
                   complete formalization of an instantiation of this
                   scheme is considered for a simple object-oriented
                   language and a corresponding type soundness theorem is
                   stated. A prototype implementation based on a
                   meta-interpreter of co-SLD has been implemented.
                   Finally, we address scalability issues of the approach,
                   by sketching an instantiation able to deal with a much
                   more expressive object-oriented language.},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/ALZ0708.pdf},
  keywords = {objects,types,coinduction},
  month = jul,
  year = 2008
}
@article{AnconaDovierFI15,
  author = {Ancona, D. and
               Dovier, A.},
  title = {A Theoretical Perspective of Coinductive Logic Programming},
  journal = {Fundamenta Informaticae},
  volume = {140},
  number = {3-4},
  pages = {221--246},
  year = {2015},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/AnconaDovierFI15.pdf},
  doi = {10.3233/FI-2015-1252},
  keywords = {coinduction,logic programming},
  abstract = {{
In this paper we study the semantics of Coinductive Logic Programming and
clarify  its intrinsic computational limits, which prevent, in particular, the definition
of a complete, computable, operational semantics.
We propose a new operational semantics that  allows a simple correctness result
and the definition of a simple meta-interpreter.
We compare, and prove the equivalence, with the operational semantics
defined and used in other papers on this topic.
}}
}
@inproceedings{AnconaDagninoZucca17,
  author = {Ancona, D. and Dagnino, F. and Zucca, E.},
  title = {Generalizing inference systems by coaxioms},
  booktitle = {European Symposium on Programming, ESOP 2017},
  year = {2017},
  note = {To appear},
  ftp = {ftp://ftp.disi.unige.it/person/AnconaD/esop17.pdf},
  abstract = {{We introduce a generalized notion of inference system to support 
structural recursion on non well-founded datatypes.
Besides  axioms and inference rules with the usual meaning, a generalized inference system
allows coaxioms, which are, intuitively, axioms which can only be applied "at infinite depth" in a proof tree. 
This notion nicely subsumes standard inference systems and their inductive and coinductive interpretation, while providing more flexibility.
Indeed, the classical results on the existence and constructive characterization of least and greatest fixed points can be extended to our generalized framework, interpreting recursive definitions as fixed points which are not necessarily the least, nor the greatest one. This allows formal reasoning in cases where the inductive and coinductive interpretation do not provide the intended meaning, or  are mixed together. 
}},
  keywords = {{coinduction}}
}

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