(*======================================================== 8 "LITTLE" LEMMAS ON qhmaps WHICH ARE USEFUL IN THE PROOF OF CLOSURE CORRECTION =========================================================*)
(* A on x0: *)

Lemma A_B_1_B_x0 : forall(m:fmap)(k:dim)(x0 y0:dart),
inv_qhmap m ->
A (B_1 (B m k x0) k y0) k x0 = nil.