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12
A Simple Model for Quotient Types
 Proceedings of TLCA'95, volume 902 of Lecture Notes in Computer Science
, 1995
"... . We give an interpretation of quotient types within in a dependent type theory with an impredicative universe of propositions (Calculus of Constructions). In the model, type dependency arises only at the propositional level, therefore universes and large eliminations cannot be interpreted. In excha ..."
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. We give an interpretation of quotient types within in a dependent type theory with an impredicative universe of propositions (Calculus of Constructions). In the model, type dependency arises only at the propositional level, therefore universes and large eliminations cannot be interpreted. In exchange, the model is much simpler and more intuitive than the one proposed by the author in [10]. Moreover, we interpret a choice operator for quotient types that, under certain restrictions, allows one to recover a representative from an equivalence class. Since the model is constructed syntactically, the interpretation function from the syntax with quotient types to the model gives rise to a procedure which eliminates quotient types by replacing propositional equality by equality relations defined by induction on the type structure ("book equalities"). 1 Introduction Intensional type theories like the Calculus of Constructions have been proposed as a framework in which to formalise mathemati...
A short and flexible proof of Strong Normalization for the Calculus of Constructions
, 1994
"... this paper can still go through (with slightly more technical effort) in case one can distinguish cases according to whether a specific subterm is a type or kind in a fixed context. The other property of type systems that is really actually required for the constructions in this paper to go through ..."
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this paper can still go through (with slightly more technical effort) in case one can distinguish cases according to whether a specific subterm is a type or kind in a fixed context. The other property of type systems that is really actually required for the constructions in this paper to go through is a slight strengthening of the Stripping property (also called Generation). This property says, for example, that if \Gamma ` v:T:M : U has a derivation D, then one can find a subderivation of
On the Definition of the Etalong Normal Form in Type Systems of the Cube
 Informal Proceedings of the Workshop on Types for Proofs and Programs
, 1993
"... The smallest transitive relation ! on welltyped normal terms such that if t is a strict subterm of u then t ! u and if T is the normal form of the type of t and the term t is not a sort then T ! t is wellfounded in the type systems of the cube. Thus every term admits a jlong normal form. Introdu ..."
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The smallest transitive relation ! on welltyped normal terms such that if t is a strict subterm of u then t ! u and if T is the normal form of the type of t and the term t is not a sort then T ! t is wellfounded in the type systems of the cube. Thus every term admits a jlong normal form. Introduction In this paper we prove that the smallest transitive relation ! on welltyped normal terms such that ffl if t is a strict subterm of u then t ! u, ffl if T is the normal form of the type of t and the term t is not a sort then T ! t is wellfounded in the type systems of the cube [1]. This result is proved using the notion of marked terms introduced by de Vrijer [6]. A motivation for this theorem is to define the jlong form of a normal term in these type systems. In simply typed calculus, to define the jlong form of a normal term we first define the jlong form of a variable x of type P 1 ! ::: ! P n ! P (P atomic) as the term [y 1 : P 1 ]:::[y n : P n ](x y 0 1 ::: y 0 n ) w...
Comparing cubes of typed and type assignment systems
 Annals of Pure and Applied Logic
, 1997
"... We study the cube of type assignment systems, as introduced in [13], and confront it with Barendregt’s typed λcube [4]. The first is obtained from the latter through applying a natural type erasing function E to derivation rules, that erases type information from terms. In particular, we address th ..."
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We study the cube of type assignment systems, as introduced in [13], and confront it with Barendregt’s typed λcube [4]. The first is obtained from the latter through applying a natural type erasing function E to derivation rules, that erases type information from terms. In particular, we address the question whether a judgement, derivable in a type assignment system, is always an erasure of a derivable judgement in a corresponding typed system; we show that this property holds only for the systems without polymorphism. The type assignment systems we consider satisfy the properties ‘subject reduction’ and ‘strong normalization’. Moreover, we define a new type assignment cube that is isomorphic to the typed one.
Dependent Types and Explicit Substitutions
, 1999
"... We present a dependenttype system for a #calculus with explicit substitutions. In this system, metavariables, as well as substitutions, are firstclass objects. We show that the system enjoys properties like type uniqueness, subject reduction, soundness, confluence and weak normalization. ..."
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We present a dependenttype system for a #calculus with explicit substitutions. In this system, metavariables, as well as substitutions, are firstclass objects. We show that the system enjoys properties like type uniqueness, subject reduction, soundness, confluence and weak normalization.
Existence and uniqueness of normal forms in pure type systems with βηconversion
 Proceedings of CSL'98, volume 1584 of Lecture Notes in Computer Science
, 1999
"... Pure Type Systems (PTS fi s) provide a parametric framework for typedcalculi `a la Church [1, 2, 10, 11]. One important aspect of PTS fi s is to feature a definitional equality based on ficonversion. In some instances however, one desires a stronger ..."
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Pure Type Systems (PTS fi s) provide a parametric framework for typedcalculi `a la Church [1, 2, 10, 11]. One important aspect of PTS fi s is to feature a definitional equality based on ficonversion. In some instances however, one desires a stronger
Equality is typable in SemiFull Pure Type Systems
 Proceedings, 25th annual IEEE symposium on Login in Computer Science (LICS ’10
, 2010
"... Abstract—There are two usual ways to describe equality in a dependent typing system, one that uses an external notion of computation like betareduction, and one that introduces a typed judgement of betaequality directly in the typing system. After being an open problem for some time, the general e ..."
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Abstract—There are two usual ways to describe equality in a dependent typing system, one that uses an external notion of computation like betareduction, and one that introduces a typed judgement of betaequality directly in the typing system. After being an open problem for some time, the general equivalence between both approaches has been solved by Adams for a class of pure type systems (PTSs) called functional. In this paper, we relax the functionality constraint and prove the equivalence for all semifull PTSs by combining the ideas of Adams with a study of the general shape of types in PTSs. As one application, an extension of this result to systems with subtyping would be a first step toward bringing closer the theory behind a proof assistant such as Coq to its implementation. I.
Variants of the Basic Calculus of Constructions
, 2004
"... In this paper, a number of different versions of the basic calculus of constructions that have appeared in the literature are compared and the exact relationships between them are determined. The biggest differences between versions are those between the original version of Coquand and the version i ..."
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In this paper, a number of different versions of the basic calculus of constructions that have appeared in the literature are compared and the exact relationships between them are determined. The biggest differences between versions are those between the original version of Coquand and the version in early papers on the subject by Seldin. None of these results is very deep, but it seems useful to collect them in one place.
On the Equational Theory of NonNormalising Pure Type Systems
, 2001
"... this paper we are chieAEy concerned with the specications U \Gamma , U and . The denitions are taken from e.g. [1] ..."
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this paper we are chieAEy concerned with the specications U \Gamma , U and . The denitions are taken from e.g. [1]
Dependent Types with Explicit Substitutions: A metatheoretical development
, 1997
"... We present a theory of dependent types with explicit substitutions. We follow a metatheoretical approach where open expressions expressions with metavariables are firstclass objects. The system enjoys properties like type uniqueness, subject reduction, soundness, confluence and weak normal ..."
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We present a theory of dependent types with explicit substitutions. We follow a metatheoretical approach where open expressions expressions with metavariables are firstclass objects. The system enjoys properties like type uniqueness, subject reduction, soundness, confluence and weak normalization.