law head_append_sym

bend-mathlib@0.8.1.0 · list.bend:2880

import Base

2880# The head of an append is the head of the first part, or else of the second, reversed to rewrite toward the simple side.
2881law head_append_sym:
2882  for -a: Quant
2883  for -A: Kind(a)
2884  for xs: List<a, A>
2885  for -ys: List<a, A>
2886  {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>}