ProofBase.append_cancel_l: law of lawful-arrays@0.1.0.0
Import: import lawful-arrays@0.1.0.0/proof_base.bend as ProofBase
Lines 501-508 of lawful-arrays@0.1.0.0/proof_base.bend: https://jend.leeeet.dev/read.txt?path=lawful-arrays@0.1.0.0/proof_base.bend&start_line=501&end_line=508

import Base

# ...and so are the second parts.
law append_cancel_l:
  for -A: Data
  for +xs: List<&2, A>
  for -y1: List<&2, A>
  for -y2: List<&2, A>
  for e: {List.append(&2, A, xs, y1) == List.append(&2, A, xs, y2) : List<&2, A>}
  {y1 == y2 : List<&2, A>}

Uses (3):
  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=lawful-arrays@0.1.0.0/proof_base.bend&name=cons_inj_t