fact: Fixpoint Tpositive e:= match e with | Tbase n => n != 0 | Tpowerset e' => Tpositive e' | Tproduct e' e'' => (Tpositive e') && (Tpositive e'') end.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq)