String.internal_append_assoc: def of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/string.bend as String
Lines 35-41 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=35&end_line=41

import Base

def internal_append_assoc(a: String, -b: String, -c: String) -> {String.append(a, String.append(b, c)) == String.append(String.append(a, b), c) : String}:
  match a:
    case SNil{}:
      {==}
    case SCon{+h, +t}:
      %internal_append_assoc(t, b, c) : {SCon{h, String.append(t, String.append(b, c))} == SCon{h, _} : String}
      {==}

Uses (2):
  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