List.map_append: law of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/list.bend as List
Lines 194-201 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=194&end_line=201

import Base

# Mapping over an append maps each part: map f (xs ++ ys) = map f xs ++ map f ys.
law map_append:
  for ~A: Type
  for ~B: Type
  for ~f: A -> B
  for xs: List<A>
  for -ys: List<A>
  {List.map(~A, ~B, ~f, List.append(&1, A, xs, ys)) == List.append(&1, B, List.map(~A, ~B, ~f, xs), List.map(~A, ~B, ~f, ys)) : List<B>}

Uses (3):
  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.map