Canonical pseries_group : {group gT} := group pseries_group_set.Local Notation ConsPred p := (@Cons nat_pred p%N) (only parsing).Implicit Types (A : {set aT}) (G H : {group aT}).

Lemma pseries_rcons_id pis pi gT (G : {group gT}) : pseries (rcons (rcons pis pi) pi) G = pseries (rcons pis pi) G.