fact: Fixpoint pred (a:T2) : option T2 := match a with zero => None | gcons zero zero 0 zero => Some zero | gcons zero zero (S n) zero => Some (gcons zero zero n zero) | gcons a b n c => (match (pred c) with Some c' => Some (gcons a b n c') | None => None end) end.
imports: Coq(Arith Compare_dec Relations Wellfounded Lia) hydras(More_Arith Restriction T1 OrdNotations Compat815)