List.head_append: law of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/list.bend as List
Lines 1647-1653 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=1647&end_line=1653

import Base

# The head of an append is the head of the first part, or else of the second.
law head_append:
  for -a: Quant
  for -A: Kind(a)
  for xs: List<a, A>
  for -ys: List<a, A>
  {List.head(a, A, List.append(a, A, xs, ys)) == Maybe.or(a, A, List.head(a, A, xs), List.head(a, A, ys)) : Maybe<a, A>}

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=List.append
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.head
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Maybe
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Maybe.or