nLab calculus of constructions

Contents

Context

Type theory

natural deduction metalanguage, practical foundations

  1. type formation rule
  2. term introduction rule
  3. term elimination rule
  4. computation rule

type theory (dependent, intensional, observational type theory, homotopy type theory)

syntax object language

computational trinitarianism =
propositions as types +programs as proofs +relation type theory/category theory

logicset theory (internal logic of)category theorytype theory
propositionsetobjecttype
predicatefamily of setsdisplay morphismdependent type
proofelementgeneralized elementterm/program
cut rulecomposition of classifying morphisms / pullback of display mapssubstitution
cut elimination for implicationcounit for hom-tensor adjunctionbeta reduction
introduction rule for implicationunit for hom-tensor adjunctioneta conversion
truesingletonterminal object/(-2)-truncated objecth-level 0-type/unit type
falseempty setinitial objectempty type
proposition, truth valuesubsingletonsubterminal object/(-1)-truncated objecth-proposition, mere proposition
logical conjunctioncartesian productproductproduct type
disjunctiondisjoint union (support of)coproduct ((-1)-truncation of)sum type (bracket type of)
implicationfunction setinternal homfunction type
negationfunction set into empty setinternal hom into initial objectfunction type into empty type
universal quantificationindexed cartesian productdependent productdependent product type
existential quantificationindexed disjoint union (support of)dependent sum ((-1)-truncation of)dependent sum type (bracket type of)
logical equivalencebijectionisomorphism/adjoint equivalenceequivalence of types
support setsupport object/(-1)-truncationpropositional truncation/bracket type
n-image of morphism into terminal object/n-truncationn-truncation modality
equalitydiagonal function/diagonal subset/diagonal relationpath space objectidentity type/path type
completely presented setsetdiscrete object/0-truncated objecth-level 2-type/set/h-set
setset with equivalence relationinternal 0-groupoidBishop set/setoid with its pseudo-equivalence relation an actual equivalence relation
equivalence class/quotient setquotientquotient type
inductioncolimitinductive type, W-type, M-type
higher inductionhigher colimithigher inductive type
-0-truncated higher colimitquotient inductive type
coinductionlimitcoinductive type
presettype without identity types
set of truth valuessubobject classifiertype of propositions
domain of discourseuniverseobject classifiertype universe
modalityclosure operator, (idempotent) monadmodal type theory, monad (in computer science)
linear logic(symmetric, closed) monoidal categorylinear type theory/quantum computation
proof netstring diagramquantum circuit
(absence of) contraction rule(absence of) diagonalno-cloning theorem
synthetic mathematicsdomain specific embedded programming language

homotopy levels

semantics

Foundations

foundations

The basis of it all

 Set theory

set theory

Foundational axioms

foundational axiom

Removing axioms

Contents

Idea

The Calculus of Constructions (CoC) is a type theory formal system for constructive proof in natural deduction style. This calculus goes back to Thierry Coquand and Gérard Huet

When supplemented by inductive types, it become the Calculus of Inductive Constructions (CIC). Sometimes coinductive types are included as well and one speaks of the Calculus of (co)inductive Constructions. This is what the Coq software implements.

More in detail, the Calculus of (co)Inductive Constructions is

  1. a pure type system, hence

    1. a system of natural deduction with dependent types;

    2. with the natural-deduction rule for dependent product types specified;

  2. with a rule for how to introduce new natural-deduction rules for arbitrary (co)inductive types.

  3. and with universes:

    a cumulative hierarchy of predicative types of types

    and an impredicative type of propositions.

All of the other standard type formations are subsumed by the existence of arbitrary inductive types, notably the empty type, dependent sum types and identity types are special inductive types. Specifying these hence makes the calculus of constructions be an intensional dependent type theory.

References

Original articles include

Surveys include

A categorical semantics for CoC is discussed in

  • Martin Hyland, Andy Pitts, The Theory of Constructions: Categorical Semantics and Topos-theoretic Models , Cont. Math. 92 (1989) pp.137-199. (draft)

For specifics of the implementation in Coq see

Last revised on September 4, 2020 at 10:41:45. See the history of this page for a list of all contributions to it.