List.foldl_append_sym: law of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/list.bend as List
Lines 2469-2478 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=2469&end_line=2478

import Base

# A left fold over an append folds the second part from the fold of the first, reversed to rewrite toward the simple side.
law foldl_append_sym:
  for ~a: Quant
  for ~A: Kind(a)
  for ~B: Type
  for ~f: B -> A -> B
  for xs: List<a, A>
  for -ys: List<a, A>
  for -z: B
  {List.foldl(~a, ~A, ~B, ~f, ys, List.foldl(~a, ~A, ~B, ~f, xs, z)) == List.foldl(~a, ~A, ~B, ~f, List.append(a, A, xs, ys), z) : B}

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.foldl
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/list.bend&name=foldl_append