proposition: Lemma formula_val_rec X x: formulap x -> formula_val X x = formula_val_aux X x (Lg (small_formulas (formula_len x)) (formula_val X)).
proof: Proof. exact:(stratified_formula_rec (formula_val_aux X)). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)