def perm_cons

bend-mathlib@0.8.1.0 · perm.bend:57

import Base
import bendlib-kernel-list@1.0.0.0/list.bend as K

57# Prepending the same element preserves permutation.
58def perm_cons(-A: Data, +x: A, +xs: List<&2, A>, -ys: List<&2, A>, h: K.perm(A, xs, ys)) -> K.perm(A, x <> xs, x <> ys):
59  (s, e) = h
60  +s = s
61  (internal_shift(s), internal_cons_eq(A, s, x, xs, ys, e))