Perm.perm_cons: def of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/perm.bend as Perm
Lines 57-61 of bend-mathlib@0.8.1.0/perm.bend: https://jend.leeeet.dev/read.txt?path=bend-mathlib@0.8.1.0/perm.bend&start_line=57&end_line=61

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

# Prepending the same element preserves permutation.
def 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):
  (s, e) = h
  +s = s
  (internal_shift(s), internal_cons_eq(A, s, x, xs, ys, e))

Uses (5):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Sigma
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/perm.bend&name=internal_cons_eq
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/perm.bend&name=internal_shift
  https://jend.leeeet.dev/definition.txt?path=bendlib-kernel-list@1.0.0.0/list.bend&name=perm