| Step | Hyp | Ref
 | Expression | 
| 1 |   | inss2 3384 | 
. . . . . 6
⊢ ((dom
𝐹 ∩ dom 𝐺) ∩ 𝐷) ⊆ 𝐷 | 
| 2 | 1 | sseli 3179 | 
. . . . 5
⊢ (𝑥 ∈ ((dom 𝐹 ∩ dom 𝐺) ∩ 𝐷) → 𝑥 ∈ 𝐷) | 
| 3 |   | fvres 5582 | 
. . . . . 6
⊢ (𝑥 ∈ 𝐷 → ((𝐹 ↾ 𝐷)‘𝑥) = (𝐹‘𝑥)) | 
| 4 |   | fvres 5582 | 
. . . . . 6
⊢ (𝑥 ∈ 𝐷 → ((𝐺 ↾ 𝐷)‘𝑥) = (𝐺‘𝑥)) | 
| 5 | 3, 4 | oveq12d 5940 | 
. . . . 5
⊢ (𝑥 ∈ 𝐷 → (((𝐹 ↾ 𝐷)‘𝑥)𝑅((𝐺 ↾ 𝐷)‘𝑥)) = ((𝐹‘𝑥)𝑅(𝐺‘𝑥))) | 
| 6 | 2, 5 | syl 14 | 
. . . 4
⊢ (𝑥 ∈ ((dom 𝐹 ∩ dom 𝐺) ∩ 𝐷) → (((𝐹 ↾ 𝐷)‘𝑥)𝑅((𝐺 ↾ 𝐷)‘𝑥)) = ((𝐹‘𝑥)𝑅(𝐺‘𝑥))) | 
| 7 | 6 | mpteq2ia 4119 | 
. . 3
⊢ (𝑥 ∈ ((dom 𝐹 ∩ dom 𝐺) ∩ 𝐷) ↦ (((𝐹 ↾ 𝐷)‘𝑥)𝑅((𝐺 ↾ 𝐷)‘𝑥))) = (𝑥 ∈ ((dom 𝐹 ∩ dom 𝐺) ∩ 𝐷) ↦ ((𝐹‘𝑥)𝑅(𝐺‘𝑥))) | 
| 8 |   | inindi 3380 | 
. . . . 5
⊢ (𝐷 ∩ (dom 𝐹 ∩ dom 𝐺)) = ((𝐷 ∩ dom 𝐹) ∩ (𝐷 ∩ dom 𝐺)) | 
| 9 |   | incom 3355 | 
. . . . 5
⊢ ((dom
𝐹 ∩ dom 𝐺) ∩ 𝐷) = (𝐷 ∩ (dom 𝐹 ∩ dom 𝐺)) | 
| 10 |   | dmres 4967 | 
. . . . . 6
⊢ dom
(𝐹 ↾ 𝐷) = (𝐷 ∩ dom 𝐹) | 
| 11 |   | dmres 4967 | 
. . . . . 6
⊢ dom
(𝐺 ↾ 𝐷) = (𝐷 ∩ dom 𝐺) | 
| 12 | 10, 11 | ineq12i 3362 | 
. . . . 5
⊢ (dom
(𝐹 ↾ 𝐷) ∩ dom (𝐺 ↾ 𝐷)) = ((𝐷 ∩ dom 𝐹) ∩ (𝐷 ∩ dom 𝐺)) | 
| 13 | 8, 9, 12 | 3eqtr4ri 2228 | 
. . . 4
⊢ (dom
(𝐹 ↾ 𝐷) ∩ dom (𝐺 ↾ 𝐷)) = ((dom 𝐹 ∩ dom 𝐺) ∩ 𝐷) | 
| 14 |   | eqid 2196 | 
. . . 4
⊢ (((𝐹 ↾ 𝐷)‘𝑥)𝑅((𝐺 ↾ 𝐷)‘𝑥)) = (((𝐹 ↾ 𝐷)‘𝑥)𝑅((𝐺 ↾ 𝐷)‘𝑥)) | 
| 15 | 13, 14 | mpteq12i 4121 | 
. . 3
⊢ (𝑥 ∈ (dom (𝐹 ↾ 𝐷) ∩ dom (𝐺 ↾ 𝐷)) ↦ (((𝐹 ↾ 𝐷)‘𝑥)𝑅((𝐺 ↾ 𝐷)‘𝑥))) = (𝑥 ∈ ((dom 𝐹 ∩ dom 𝐺) ∩ 𝐷) ↦ (((𝐹 ↾ 𝐷)‘𝑥)𝑅((𝐺 ↾ 𝐷)‘𝑥))) | 
| 16 |   | resmpt3 4995 | 
. . 3
⊢ ((𝑥 ∈ (dom 𝐹 ∩ dom 𝐺) ↦ ((𝐹‘𝑥)𝑅(𝐺‘𝑥))) ↾ 𝐷) = (𝑥 ∈ ((dom 𝐹 ∩ dom 𝐺) ∩ 𝐷) ↦ ((𝐹‘𝑥)𝑅(𝐺‘𝑥))) | 
| 17 | 7, 15, 16 | 3eqtr4ri 2228 | 
. 2
⊢ ((𝑥 ∈ (dom 𝐹 ∩ dom 𝐺) ↦ ((𝐹‘𝑥)𝑅(𝐺‘𝑥))) ↾ 𝐷) = (𝑥 ∈ (dom (𝐹 ↾ 𝐷) ∩ dom (𝐺 ↾ 𝐷)) ↦ (((𝐹 ↾ 𝐷)‘𝑥)𝑅((𝐺 ↾ 𝐷)‘𝑥))) | 
| 18 |   | offval3 6191 | 
. . 3
⊢ ((𝐹 ∈ 𝑉 ∧ 𝐺 ∈ 𝑊) → (𝐹 ∘𝑓 𝑅𝐺) = (𝑥 ∈ (dom 𝐹 ∩ dom 𝐺) ↦ ((𝐹‘𝑥)𝑅(𝐺‘𝑥)))) | 
| 19 | 18 | reseq1d 4945 | 
. 2
⊢ ((𝐹 ∈ 𝑉 ∧ 𝐺 ∈ 𝑊) → ((𝐹 ∘𝑓 𝑅𝐺) ↾ 𝐷) = ((𝑥 ∈ (dom 𝐹 ∩ dom 𝐺) ↦ ((𝐹‘𝑥)𝑅(𝐺‘𝑥))) ↾ 𝐷)) | 
| 20 |   | resexg 4986 | 
. . 3
⊢ (𝐹 ∈ 𝑉 → (𝐹 ↾ 𝐷) ∈ V) | 
| 21 |   | resexg 4986 | 
. . 3
⊢ (𝐺 ∈ 𝑊 → (𝐺 ↾ 𝐷) ∈ V) | 
| 22 |   | offval3 6191 | 
. . 3
⊢ (((𝐹 ↾ 𝐷) ∈ V ∧ (𝐺 ↾ 𝐷) ∈ V) → ((𝐹 ↾ 𝐷) ∘𝑓 𝑅(𝐺 ↾ 𝐷)) = (𝑥 ∈ (dom (𝐹 ↾ 𝐷) ∩ dom (𝐺 ↾ 𝐷)) ↦ (((𝐹 ↾ 𝐷)‘𝑥)𝑅((𝐺 ↾ 𝐷)‘𝑥)))) | 
| 23 | 20, 21, 22 | syl2an 289 | 
. 2
⊢ ((𝐹 ∈ 𝑉 ∧ 𝐺 ∈ 𝑊) → ((𝐹 ↾ 𝐷) ∘𝑓 𝑅(𝐺 ↾ 𝐷)) = (𝑥 ∈ (dom (𝐹 ↾ 𝐷) ∩ dom (𝐺 ↾ 𝐷)) ↦ (((𝐹 ↾ 𝐷)‘𝑥)𝑅((𝐺 ↾ 𝐷)‘𝑥)))) | 
| 24 | 17, 19, 23 | 3eqtr4a 2255 | 
1
⊢ ((𝐹 ∈ 𝑉 ∧ 𝐺 ∈ 𝑊) → ((𝐹 ∘𝑓 𝑅𝐺) ↾ 𝐷) = ((𝐹 ↾ 𝐷) ∘𝑓 𝑅(𝐺 ↾ 𝐷))) |