def length_zero_nil

bend-collections-laws-math@1.0.0.0 · proofs/lib/list.bend:144

import Base
import bend-collections-laws-math@1.0.0.0/proofs/lib/nat.bend as N
import bend-collections-laws-math@1.0.0.0/spec/lib/common.bend as SC

144def length_zero_nil(-A: Data, +xs: List<&2, A>, +h: {SC.length(A, xs) == 0n : Nat}) -> {xs == Nil{} : List<&2, A>}:
145  match xs:
146    case Nil{}:
147      {==}
148    case Con{x, t}:
149      Empty.absurd({Con{x, t} == Nil{} : List<&2, A>}, N.succ_zero(SC.length(A, t), h))