List.head_map_sym: law of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/list.bend as List
Lines 2891-2897 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=2891&end_line=2897

import Base

# The head of a map is the mapped head, reversed to rewrite toward the simple side.
law head_map_sym:
  for ~A: Type
  for ~B: Type
  for ~f: A -> B
  for xs: List<A>
  {Maybe.map(&1, A, B, f, List.head(&1, A, xs)) == List.head(&1, B, List.map(~A, ~B, ~f, xs)) : Maybe<&1, B>}

Uses (7):
  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.head
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.map
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Maybe
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Maybe.map
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/list.bend&name=head_map