| Step | Hyp | Ref
 | Expression | 
| 1 |   | dfss2 3172 | 
. 2
⊢ ((𝐹 “ 𝐴) ⊆ 𝐵 ↔ ∀𝑦(𝑦 ∈ (𝐹 “ 𝐴) → 𝑦 ∈ 𝐵)) | 
| 2 |   | vex 2766 | 
. . . . . . . . 9
⊢ 𝑦 ∈ V | 
| 3 | 2 | elima 5014 | 
. . . . . . . 8
⊢ (𝑦 ∈ (𝐹 “ 𝐴) ↔ ∃𝑥 ∈ 𝐴 𝑥𝐹𝑦) | 
| 4 |   | eqcom 2198 | 
. . . . . . . . . 10
⊢ (𝑦 = (𝐹‘𝑥) ↔ (𝐹‘𝑥) = 𝑦) | 
| 5 |   | ssel 3177 | 
. . . . . . . . . . . 12
⊢ (𝐴 ⊆ dom 𝐹 → (𝑥 ∈ 𝐴 → 𝑥 ∈ dom 𝐹)) | 
| 6 |   | funbrfvb 5603 | 
. . . . . . . . . . . . 13
⊢ ((Fun
𝐹 ∧ 𝑥 ∈ dom 𝐹) → ((𝐹‘𝑥) = 𝑦 ↔ 𝑥𝐹𝑦)) | 
| 7 | 6 | ex 115 | 
. . . . . . . . . . . 12
⊢ (Fun
𝐹 → (𝑥 ∈ dom 𝐹 → ((𝐹‘𝑥) = 𝑦 ↔ 𝑥𝐹𝑦))) | 
| 8 | 5, 7 | syl9 72 | 
. . . . . . . . . . 11
⊢ (𝐴 ⊆ dom 𝐹 → (Fun 𝐹 → (𝑥 ∈ 𝐴 → ((𝐹‘𝑥) = 𝑦 ↔ 𝑥𝐹𝑦)))) | 
| 9 | 8 | imp31 256 | 
. . . . . . . . . 10
⊢ (((𝐴 ⊆ dom 𝐹 ∧ Fun 𝐹) ∧ 𝑥 ∈ 𝐴) → ((𝐹‘𝑥) = 𝑦 ↔ 𝑥𝐹𝑦)) | 
| 10 | 4, 9 | bitrid 192 | 
. . . . . . . . 9
⊢ (((𝐴 ⊆ dom 𝐹 ∧ Fun 𝐹) ∧ 𝑥 ∈ 𝐴) → (𝑦 = (𝐹‘𝑥) ↔ 𝑥𝐹𝑦)) | 
| 11 | 10 | rexbidva 2494 | 
. . . . . . . 8
⊢ ((𝐴 ⊆ dom 𝐹 ∧ Fun 𝐹) → (∃𝑥 ∈ 𝐴 𝑦 = (𝐹‘𝑥) ↔ ∃𝑥 ∈ 𝐴 𝑥𝐹𝑦)) | 
| 12 | 3, 11 | bitr4id 199 | 
. . . . . . 7
⊢ ((𝐴 ⊆ dom 𝐹 ∧ Fun 𝐹) → (𝑦 ∈ (𝐹 “ 𝐴) ↔ ∃𝑥 ∈ 𝐴 𝑦 = (𝐹‘𝑥))) | 
| 13 | 12 | imbi1d 231 | 
. . . . . 6
⊢ ((𝐴 ⊆ dom 𝐹 ∧ Fun 𝐹) → ((𝑦 ∈ (𝐹 “ 𝐴) → 𝑦 ∈ 𝐵) ↔ (∃𝑥 ∈ 𝐴 𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵))) | 
| 14 |   | r19.23v 2606 | 
. . . . . 6
⊢
(∀𝑥 ∈
𝐴 (𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵) ↔ (∃𝑥 ∈ 𝐴 𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵)) | 
| 15 | 13, 14 | bitr4di 198 | 
. . . . 5
⊢ ((𝐴 ⊆ dom 𝐹 ∧ Fun 𝐹) → ((𝑦 ∈ (𝐹 “ 𝐴) → 𝑦 ∈ 𝐵) ↔ ∀𝑥 ∈ 𝐴 (𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵))) | 
| 16 | 15 | albidv 1838 | 
. . . 4
⊢ ((𝐴 ⊆ dom 𝐹 ∧ Fun 𝐹) → (∀𝑦(𝑦 ∈ (𝐹 “ 𝐴) → 𝑦 ∈ 𝐵) ↔ ∀𝑦∀𝑥 ∈ 𝐴 (𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵))) | 
| 17 | 16 | ancoms 268 | 
. . 3
⊢ ((Fun
𝐹 ∧ 𝐴 ⊆ dom 𝐹) → (∀𝑦(𝑦 ∈ (𝐹 “ 𝐴) → 𝑦 ∈ 𝐵) ↔ ∀𝑦∀𝑥 ∈ 𝐴 (𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵))) | 
| 18 |   | ralcom4 2785 | 
. . . 4
⊢
(∀𝑥 ∈
𝐴 ∀𝑦(𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵) ↔ ∀𝑦∀𝑥 ∈ 𝐴 (𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵)) | 
| 19 |   | ssel2 3178 | 
. . . . . . . . 9
⊢ ((𝐴 ⊆ dom 𝐹 ∧ 𝑥 ∈ 𝐴) → 𝑥 ∈ dom 𝐹) | 
| 20 | 19 | anim2i 342 | 
. . . . . . . 8
⊢ ((Fun
𝐹 ∧ (𝐴 ⊆ dom 𝐹 ∧ 𝑥 ∈ 𝐴)) → (Fun 𝐹 ∧ 𝑥 ∈ dom 𝐹)) | 
| 21 | 20 | 3impb 1201 | 
. . . . . . 7
⊢ ((Fun
𝐹 ∧ 𝐴 ⊆ dom 𝐹 ∧ 𝑥 ∈ 𝐴) → (Fun 𝐹 ∧ 𝑥 ∈ dom 𝐹)) | 
| 22 |   | funfvex 5575 | 
. . . . . . 7
⊢ ((Fun
𝐹 ∧ 𝑥 ∈ dom 𝐹) → (𝐹‘𝑥) ∈ V) | 
| 23 |   | nfv 1542 | 
. . . . . . . 8
⊢
Ⅎ𝑦(𝐹‘𝑥) ∈ 𝐵 | 
| 24 |   | eleq1 2259 | 
. . . . . . . 8
⊢ (𝑦 = (𝐹‘𝑥) → (𝑦 ∈ 𝐵 ↔ (𝐹‘𝑥) ∈ 𝐵)) | 
| 25 | 23, 24 | ceqsalg 2791 | 
. . . . . . 7
⊢ ((𝐹‘𝑥) ∈ V → (∀𝑦(𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵) ↔ (𝐹‘𝑥) ∈ 𝐵)) | 
| 26 | 21, 22, 25 | 3syl 17 | 
. . . . . 6
⊢ ((Fun
𝐹 ∧ 𝐴 ⊆ dom 𝐹 ∧ 𝑥 ∈ 𝐴) → (∀𝑦(𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵) ↔ (𝐹‘𝑥) ∈ 𝐵)) | 
| 27 | 26 | 3expa 1205 | 
. . . . 5
⊢ (((Fun
𝐹 ∧ 𝐴 ⊆ dom 𝐹) ∧ 𝑥 ∈ 𝐴) → (∀𝑦(𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵) ↔ (𝐹‘𝑥) ∈ 𝐵)) | 
| 28 | 27 | ralbidva 2493 | 
. . . 4
⊢ ((Fun
𝐹 ∧ 𝐴 ⊆ dom 𝐹) → (∀𝑥 ∈ 𝐴 ∀𝑦(𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵) ↔ ∀𝑥 ∈ 𝐴 (𝐹‘𝑥) ∈ 𝐵)) | 
| 29 | 18, 28 | bitr3id 194 | 
. . 3
⊢ ((Fun
𝐹 ∧ 𝐴 ⊆ dom 𝐹) → (∀𝑦∀𝑥 ∈ 𝐴 (𝑦 = (𝐹‘𝑥) → 𝑦 ∈ 𝐵) ↔ ∀𝑥 ∈ 𝐴 (𝐹‘𝑥) ∈ 𝐵)) | 
| 30 | 17, 29 | bitrd 188 | 
. 2
⊢ ((Fun
𝐹 ∧ 𝐴 ⊆ dom 𝐹) → (∀𝑦(𝑦 ∈ (𝐹 “ 𝐴) → 𝑦 ∈ 𝐵) ↔ ∀𝑥 ∈ 𝐴 (𝐹‘𝑥) ∈ 𝐵)) | 
| 31 | 1, 30 | bitrid 192 | 
1
⊢ ((Fun
𝐹 ∧ 𝐴 ⊆ dom 𝐹) → ((𝐹 “ 𝐴) ⊆ 𝐵 ↔ ∀𝑥 ∈ 𝐴 (𝐹‘𝑥) ∈ 𝐵)) |