proposition: Lemma weq_card e e' : e ≡ e' -> #|e| = #|e'|.
proof: Proof. rewrite weq_spec (rwP eqP) eqn_leq => [[A B]]. by rewrite !leq_card. Qed.
imports: Setoid Morphisms kat normalisation rewriting kat_tac comparisons rel relalg boolean mathcomp(all_ssreflect)