fact: Definition cforall N T : env N -> (env T -> Type) -> Type := env_rect (@^~ Empty) (fun _ e IHe e' IHe' R => forall x, IHe (fun xe => IHe' (R \o ENode x xe))).
imports: HB(structures) BinPos BinNat mathcomp(ssreflect ssrbool ssrfun ssrnat eqtype seq bigop)