∀ {𝕜 : Type u_1} [inst : NontriviallyNormedField 𝕜] {E : Type u_2} [inst_1 : NormedAddCommGroup E]
  [inst_2 : NormedSpace 𝕜 E] {H : Type u_3} [inst_3 : TopologicalSpace H] {I : ModelWithCorners 𝕜 E H} {M : Type u_4}
  [inst_4 : TopologicalSpace M] [inst_5 : ChartedSpace H M] {E' : Type u_5} [inst_6 : NormedAddCommGroup E']
  [inst_7 : NormedSpace 𝕜 E'] {z : M} {f g : M → E'} {f' g' : TangentSpace I z →L[𝕜] E'},
  HasMFDerivAt I (modelWithCornersSelf 𝕜 E') f z f' →
    HasMFDerivAt I (modelWithCornersSelf 𝕜 E') g z g' → HasMFDerivAt I (modelWithCornersSelf 𝕜 E') (f + g) z (f' + g')