fact: Fixpoint n2s n m := match n with 0%nat => ""%string | S n1 => if m =? 0 then iter n (fun l => " " ++ l)%string ""%string else ((n2s n1 (m / 10)%N) ++ (String (d2a (m mod 10)%N) ""))%string end.
imports: Ascii String List EqNat NArith