∀ {L : FirstOrder.Language} {M : Type u_4} {N : Type u_1} [inst : L.Structure M] [inst_1 : L.Structure N]
  (f : L.Embedding M N) (s : L.Substructure M) (x : ↥(FirstOrder.Language.Substructure.map f.toHom s)),
  (FirstOrder.Language.Embedding.codRestrict (FirstOrder.Language.Substructure.map f.toHom s) (f.domRestrict s) ⋯)
      ⟨Classical.choose ⋯, ⋯⟩ =
    x