∀ {L : FirstOrder.Language} {M : Type w} {N : Type w'} [inst : L.Structure M] [inst_1 : L.Structure N]
  {f g : L.PartialEquiv M N} (h : f ≤ g) (x : ↥f.dom),
  g.toEquiv ((FirstOrder.Language.Substructure.inclusion ⋯) x) =
    (FirstOrder.Language.Substructure.inclusion ⋯) (f.toEquiv x)