String.append_assoc: law of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/string.bend as String
Lines 43-48 of bend-mathlib@0.8.1.0/string.bend: https://jend.leeeet.dev/read.txt?path=bend-mathlib@0.8.1.0/string.bend&start_line=43&end_line=48

import Base

# Append is associative: (a ++ b) ++ c = a ++ (b ++ c).
law append_assoc:
  for a: String
  for -b: String
  for -c: String
  {String.append(String.append(a, b), c) == String.append(a, String.append(b, c)) : String}

Uses (4):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Equal.sym
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=String
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=String.append
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/string.bend&name=internal_append_assoc