List.append_cons: law of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/list.bend as List
Lines 448-455 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=448&end_line=455

import Base

# Appending after a cons: (x :: xs) ++ ys = x :: (xs ++ ys).
law append_cons:
  for -a: Quant
  for -A: Kind(a)
  for -x: A
  for -xs: List<a, A>
  for -ys: List<a, A>
  {List.append(a, A, x <> xs, ys) == x <> List.append(a, A, xs, ys) : List<a, A>}

Uses (2):
  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