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_unpack': forall j j', age (m_phi j) (m_phi j') /\ m_dry j = m_dry j' -> age1_juicy_mem j = Some j'.