| ⊢ | f ; g ∧ f (g ⊃ g1) ⊃ f ; g1 | ChopAndYieldsMP | 
Proof:
| 1 | ⊢ f ; g ∧ f  (g  ⊃ g1) ⊃ f ; (g ∧ (g  ⊃ g1)) | |
| 2  | ⊢ g ∧ (g  ⊃ g1) ⊃ g1                                    | |
| 3  | ⊢ f ; (g ∧ (g  ⊃ g1)) ⊃ f ; g1                       | |
| 4  | ⊢ f ; g ∧ f  (g  ⊃ g1) ⊃ f ; g1                      | 
qed