law head_append

bend-mathlib@0.8.1.0 · list.bend:1647

import Base

1647# The head of an append is the head of the first part, or else of the second.
1648law head_append:
1649  for -a: Quant
1650  for -A: Kind(a)
1651  for xs: List<a, A>
1652  for -ys: List<a, A>
1653  {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>}