#[local] Instance Op_max_length : ZifyClasses.CstOp max_length :=
  { TCst := 16777211%Z ; TCstInj := eq_refl }.#[local] Ltac case_if :=
  lazymatch goal with
  | |- context C [if ?b then _ else _] => destruct b eqn:?
  | H : context C [if ?b then _ else _] |- _ => destruct b eqn:?
  end.

Lemma char63_compare_trans (c1 c2 c3 : char63) (c : comparison) : char63_compare c1 c2 = c -> char63_compare c2 c3 = c -> char63_compare c1 c3 = c.