proposition: Lemma predC_itvl a : [predC Interval -oo a] =i Interval a +oo.
proof: Proof. case: a => [b x|[]//] y. by rewrite !inE !subitvE/= bnd_simp andbT !lteBSide/= lteifNE negbK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(div fintype bigop order ssralg finset fingroup) mathcomp(ssrnum)