package anders

Anders

Homotopy Type System with Strict Equality.

Features

• Homepage: https://groupoid.space/homotopy
• Fibrant MLTT-style ΠΣ primitives with strict equality in 500 LOC
• Cofibrant CHM-style I primitives with pretypes hierarchy Vₙ in 500 LOC
• Generalized Transport and Homogeneous Composition core Kan operations
• Partial Elements
• Cubical Subtypes
• Strict Equality on pretypes
• Parser in 80 LOC
• Lexer in 80 LOC
• UTF-8 support including universe levels
• Lean syntax for ΠΣ
• 1D syntax with top-level declarations
• Groupoid Infinity CCHM base library: https://groupoid.space/math
• Best suited for academic papers and fast type checking

Setup

$ opam install anders

Samples

You 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 ∨ j ∨ k)
          (λ (i : I), [(j = 0) → a,
                       (j = 1) → p @ -i ∧ -k,
                       (k = 1) → a])
          (inc (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 ∨ -i) (λ (j : I), [(i = 0) → p @ j, (i = 1) → q @ j]) (inc (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), [(φ : r = 1) → transp (<j> A (i ∨ j)) i (u i φ)])
                  (inc (transp (<i> A i) 0 (ouc u₀)))

$ anders check path.anders

CCHM

Anders was built by strictly following these publications:

• Cubical Type Theory: a constructive interpretation of the univalence axiom [Cohen, Coquand, Huber, Mörtberg]
• On Higher Inductive Types in Cubical Type Theory [Coquand, Huber, Mörtberg]
• Canonicity for Cubical Type Theory [Huber]
• Canonicity and homotopy canonicity for cubical type theory [Coquand, Huber, Sattler]
• Cubical Synthetic Homotopy Theory [Mörtberg, Pujet]
• Unifying Cubical Models of Univalent Type Theory [Cavallo, Mörtberg, Swan]
• Cubical Agda: A Dependently Typed PL with Univalence and HITs [Vezzosi, Mörtberg, Abel]
• A Cubical Type Theory for Higher Inductive Types [Huber]
• Gluing for type theory [Kaposi, Huber, Sattler]
• Cubical Methods in HoTT/UF [Mörtberg]

We tried to bring in as little of ourselves as possible.

HTS

Type system with two identities.

• A simple type system with two identity types [Voevodsky]
• Two-level type theory and applications [Annenkov, Capriotti, Kraus, Sattler]
• Syntax for two-level type theory [Bonacina, Ahrens]

Benchmarks

$ time make
real    0m1.254s
user    0m0.981s
sys     0m0.183s

$ time for i in lib/* ; do ./anders.native check $i ; done
real    0m0.083s
user    0m0.080s
sys     0m0.004s

Acknowledgements

• Univalent People

Authors

• Siegmentation Fault
• 5HT