BendMlNatLemmas.length_append: law of bend-ml-nat-lemmas@0.1.2.0
Import: import bend-ml-nat-lemmas@0.1.2.0/main.bend as BendMlNatLemmas
Lines 258-262 of bend-ml-nat-lemmas@0.1.2.0/main.bend: https://jend.leeeet.dev/read.txt?path=bend-ml-nat-lemmas@0.1.2.0/main.bend&start_line=258&end_line=262

import Base

law length_append:
  for -A: Data
  for  xs: List<&2, A>
  for  ys: List<&2, A>
  {List.length(&2, A, List.append(&2, A, xs, ys)) == Nat.add(List.length(&2, A, xs), List.length(&2, A, ys)) : Nat}

Uses (5):
  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.length
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.add