List.contains_append: law of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/list.bend as List
Lines 665-672 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=665&end_line=672

import Base

# An append contains x iff either part does.
law contains_append:
  for ~A: Data
  for ~eq: A -> A -> Bool
  for xs: List<&2, A>
  for -ys: List<&2, A>
  for +x: A
  {List.contains(~A, ~eq, List.append(&2, A, xs, ys), x) == Bool.or(List.contains(~A, ~eq, xs, x), List.contains(~A, ~eq, ys, x)) : Bool}

Uses (6):
  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=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=internal_contains_cons_or