Modal Homotopy Type System.
type exp =
| EPre of Z.t | EKan of Z.t | EVar of name | EHole (* cosmos *)
| EPi of exp * (name * exp) | ELam of exp * (name * exp) | EApp of exp * exp (* pi *)
| ESig of exp * (name * exp) | EPair of tag * exp * exp | EFst of exp | ESnd of exp (* sigma *)
| EId of exp | ERef of exp | EJ of exp | EField of exp * string (* strict equality *)
| EPathP of exp | EPLam of exp | EAppFormula of exp * exp (* path equality *)
| EI | EDir of dir | EAnd of exp * exp | EOr of exp * exp | ENeg of exp (* CCHM interval *)
| ETransp of exp * exp | EHComp of exp * exp * exp * exp (* Kan operations *)
| EPartial of exp | EPartialP of exp * exp | ESystem of exp System.t (* partial functions *)
| ESub of exp * exp * exp | EInc of exp * exp | EOuc of exp (* cubical subtypes *)
| EGlue of exp | EGlueElem of exp * exp * exp | EUnglue of exp (* glueing *)
| EEmpty | EIndEmpty of exp (* 𝟎 *)
| EUnit | EStar | EIndUnit of exp (* 𝟏 *)
| EBool | EFalse | ETrue | EIndBool of exp (* 𝟐 *)
| EW of exp * (name * exp) | ESup of exp * exp | EIndW of exp * exp * exp (* W *)
| EIm of exp | EInf of exp | EIndIm of exp * exp | EJoin of exp (* Infinitesimal Modality *)
| ECoeq of exp | EIota of exp | EResp of exp | EIndCoeq of exp (* Coequalizer *)
| EDisc of exp | EBase of exp | EHub of exp | ESpoke of exp | EIndDisc of exp (* Disc *)$ opam install andersYou can find some examples in the share directory of the Anders package.
def comp-Path⁻¹ (A : U) (a b : A) (p : Path A a b) :
Path (Path A a a) (comp-Path A a b a p (<i> p @ -i)) (<_> a) :=
<k j> hcomp A (∂ j ∨ k) (λ (i : I), [(j = 0) → a, (j = 1) → p @ -i ∧ -k, (k = 1) → a]) (p @ j ∧ -k)
def kan (A : U) (a b c d : A) (p : Path A a c) (q : Path A b d) (r : Path A a b) : Path A c d :=
<i> hcomp A (∂ i) (λ (j : I), [(i = 0) → p @ j, (i = 1) → q @ j]) (r @ i)
def comp (A : I → U) (r : I) (u : Π (i : I), Partial (A i) r) (u₀ : (A 0)[r ↦ u 0]) : A 1 :=
hcomp (A 1) r (λ (i : I), [(r = 1) → transp (<j>A (i ∨ j)) i (u i 1=1)]) (transp(<i> A i) 0 (ouc u₀))
def ghcomp (A : U) (r : I) (u : I → Partial A r) (u₀ : A[r ↦ u 0]) : A :=
hcomp A (∂ r) (λ (j : I), [(r = 1) → u j 1=1, (r = 0) → ouc u₀]) (ouc u₀)$ anders check library/path.andersType Checker is based on classical MLTT-80 with 0, 1, 2 and W-types.
Anders was built by strictly following CCHM publications:
We tried to bring in as little of ourselves as possible.
Anders supports classical Homotopy Type System with two identities.
Infinitesimal Modality was added for direct support of Synthetic Differential Geometry.
$ time make
real 0m4.936s
user 0m1.874s
sys 0m0.670s$ time for i in library/* ; do ./anders.native check $i ; done
real 0m2.085s
user 0m1.982s
sys 0m0.105s