proposition: Lemma If_form_rf : rformula pred_f -> rformula then_f -> rformula else_f -> rformula If.
proof: Proof. by move=> /= -> -> ->. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)