∀ (motive : ByteArray.utf8DecodeChar?.FirstByte → Sort u_1)
  (h_1 :
    ByteArray.utf8DecodeChar?.FirstByte.done = ByteArray.utf8DecodeChar?.FirstByte.invalid →
      motive ByteArray.utf8DecodeChar?.FirstByte.invalid)
  (h_2 :
    ByteArray.utf8DecodeChar?.FirstByte.done = ByteArray.utf8DecodeChar?.FirstByte.done →
      motive ByteArray.utf8DecodeChar?.FirstByte.done)
  (h_3 :
    ByteArray.utf8DecodeChar?.FirstByte.done = ByteArray.utf8DecodeChar?.FirstByte.oneMore →
      motive ByteArray.utf8DecodeChar?.FirstByte.oneMore)
  (h_4 :
    ByteArray.utf8DecodeChar?.FirstByte.done = ByteArray.utf8DecodeChar?.FirstByte.twoMore →
      motive ByteArray.utf8DecodeChar?.FirstByte.twoMore)
  (h_5 :
    ByteArray.utf8DecodeChar?.FirstByte.done = ByteArray.utf8DecodeChar?.FirstByte.threeMore →
      motive ByteArray.utf8DecodeChar?.FirstByte.threeMore),
  (match h : ByteArray.utf8DecodeChar?.FirstByte.done with
    | ByteArray.utf8DecodeChar?.FirstByte.invalid => h_1 h
    | ByteArray.utf8DecodeChar?.FirstByte.done => h_2 h
    | ByteArray.utf8DecodeChar?.FirstByte.oneMore => h_3 h
    | ByteArray.utf8DecodeChar?.FirstByte.twoMore => h_4 h
    | ByteArray.utf8DecodeChar?.FirstByte.threeMore => h_5 h) =
    h_2 ⋯