law take_left_sym

bend-mathlib@0.8.1.0 · list.bend:2551

import Base

2551# Taking the length of the first part of an append gives the first part back, reversed to rewrite toward the simple side.
2552law take_left_sym:
2553  for -a: Quant
2554  for -A: Kind(a)
2555  for xs: List<a, A>
2556  for ys: List<a, A>
2557  {xs == List.take(a, A, List.append(a, A, xs, ys), List.length(a, A, xs)) : List<a, A>}