fact: Definition Derive_inv (R : Ensf) (x y : Word) := match x return Prop with | nil => False | cons A w => ex2 (fun u : Word => dans (couple A (word u)) R) (fun u : Word => ex2 (fun v : Word => cons A v = x :>Word) (fun v : Word => Append u v = y :>Word)) \/ ex2 (fun v : Word => Derive R w v) (fun v : Word => cons A v = y :>Word) end.
imports: Ensf Words more_words need fonctions Relations