(* Sewing at dimension 1 and planarity preservation: *)

Lemma expf_planar_L1: forall (m:fmap)(x y:dart),
inv_qhmap m -> planar m ->
prec_Lq m di1 x y -> let mc:= clos m in
(~eqc mc x y \/ expf mc x (A mc di0 y)) ->
planar (L m di1 x y).