Record Store : Type :=
mkStore  {index:positive;contents:Tree}.Record Store : Type :=
mkStore  {index:positive;contents:Tree}.Record Store : Type :=
mkStore  {index:positive;contents:Tree}.Record Store : Type :=
mkStore  {index:positive;contents:Tree}.Definition empty := mkStore xH Tempty.Definition push a  S :=
mkStore (Pos.succ (index S)) (Tadd (index S) a (contents S)).Definition get i S := Tget i (contents S).

Lemma get_empty : forall i, get i empty = PNone.