(* Sewing at dimension 0 and planarity preservation: *)

Lemma expf_planar_L0: forall (m:fmap)(x y:dart),
inv_qhmap m -> planar m ->
prec_Lq m di0 x y -> let mc:= clos m in
(~eqc mc x y \/ expf mc (A_1 mc di1 x) y) ->
planar (L m di0 x y).