Program Definition age1_juicy_mem (j: juicy_mem): option juicy_mem :=
      match age1 (m_phi j) with
        | Some phi' => Some (mkJuicyMem (m_dry j) phi' _ _ _ _)
        | None => None
      end.

Lemma age1_juicy_mem_Some: forall j j', age1_juicy_mem j = Some j' -> age1 (m_phi j) = Some (m_phi j').