∀ {L : FirstOrder.Language} {M : Type w} {N : Type u_1} [inst : L.Structure M] [inst_1 : L.Structure N]
  (S : L.Substructure M) {T : L.Substructure N} {f : L.Hom M N},
  FirstOrder.Language.Substructure.map f S ≤ T → S ≤ FirstOrder.Language.Substructure.comap f T