(* NEW, OK: *)

Lemma distinct_faces_Br1:
forall(m:fmap)(x x' xs xs' z z' zs zs':dart)(l:list),
inv_hmap m -> planar m ->
let l1:= cons x x' (cons xs xs' (cons z z'
(cons zs zs' l))) in
double_link_list m l1 ->
pre_ring0 m l1 ->
pre_ring3 m l1 ->
face_adjacent m x x' xs xs' ->
distinct_faces (Br1 m x x') z z' zs zs'.