Definition writable0_share (sh: share) :=
    join_sub Share.Rsh sh.

Lemma glb_split_lemma1: forall a b, Share.glb Share.Rsh a = Share.glb Share.Rsh b -> Share.glb Share.Rsh (fst (Share.split a)) = Share.glb Share.Rsh (fst (Share.split b)).