List.head_append_sym: law of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/list.bend as List
Lines 2880-2886 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=2880&end_line=2886

import Base

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

Uses (7):
  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.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
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/list.bend&name=head_append