fact: Definition FS_inj {n} (x y: t n) (eq: FS x = FS y): x = y := match eq in _ = a return match a as a' in t m return match m with |0 => Prop |S n' => t n' -> Prop end with F1 => fun _ => True |FS y => fun x' => x' = y end x with eq_refl => eq_refl end.
imports: PeanoNat