List.contains_append_sym: law of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/list.bend as List
Lines 2529-2536 of bend-mathlib@0.8.1.0/list.bend: https://jend.leeeet.dev/read.txt?path=bend-mathlib@0.8.1.0/list.bend&start_line=2529&end_line=2536

import Base

# An append contains x iff either part does, reversed to rewrite toward the simple side.
law contains_append_sym:
  for ~A: Data
  for ~eq: A -> A -> Bool
  for xs: List<&2, A>
  for -ys: List<&2, A>
  for +x: A
  {Bool.or(List.contains(~A, ~eq, xs, x), List.contains(~A, ~eq, ys, x)) == List.contains(~A, ~eq, List.append(&2, A, xs, ys), x) : Bool}

Uses (7):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool.or
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Equal.sym
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.append
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.contains
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/list.bend&name=contains_append