Definition juicy_mem_resource: forall jm m', resource_at m' = resource_at (m_phi jm) ->
  {jm' | m_phi jm' = m' /\ m_dry jm' = m_dry jm}.

Lemma writable_join_sub: forall loc phi1 phi2, join_sub phi1 phi2 -> writable loc phi1 -> writable loc phi2.