List.concat_append: law of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/list.bend as List
Lines 480-486 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=480&end_line=486

import Base

# Concatenating an append concatenates each part: concat (xss ++ yss) = concat xss ++ concat yss.
law concat_append:
  for -a: Quant
  for -A: Kind(a)
  for xss: List<a, List<a, A>>
  for -yss: List<a, List<a, A>>
  {List.concat(a, A, List.append(a, List<a, A>, xss, yss)) == List.append(a, A, List.concat(a, A, xss), List.concat(a, A, yss)) : List<a, A>}

Uses (5):
  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.concat
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/list.bend&name=append_assoc