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