| Step | Hyp | Ref
 | Expression | 
| 1 |   | df-rex 2481 | 
. . . 4
⊢
(∃𝑥 ∈
𝐴 𝑥𝐹𝑦 ↔ ∃𝑥(𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦)) | 
| 2 |   | df-rex 2481 | 
. . . . 5
⊢
(∃𝑥 ∈
𝐵 𝑥𝐹𝑦 ↔ ∃𝑥(𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) | 
| 3 | 2 | notbii 669 | 
. . . 4
⊢ (¬
∃𝑥 ∈ 𝐵 𝑥𝐹𝑦 ↔ ¬ ∃𝑥(𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) | 
| 4 |   | alnex 1513 | 
. . . . . . 7
⊢
(∀𝑥 ¬
(𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦) ↔ ¬ ∃𝑥(𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) | 
| 5 |   | 19.29r 1635 | 
. . . . . . 7
⊢
((∃𝑥(𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ∀𝑥 ¬ (𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) → ∃𝑥((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ (𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦))) | 
| 6 | 4, 5 | sylan2br 288 | 
. . . . . 6
⊢
((∃𝑥(𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ ∃𝑥(𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) → ∃𝑥((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ (𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦))) | 
| 7 |   | simpl 109 | 
. . . . . . . . 9
⊢ (((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ (𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) → (𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦)) | 
| 8 |   | simplr 528 | 
. . . . . . . . . 10
⊢ (((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ (𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) → 𝑥𝐹𝑦) | 
| 9 |   | simpr 110 | 
. . . . . . . . . . 11
⊢ (((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ (𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) → ¬ (𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) | 
| 10 |   | ancom 266 | 
. . . . . . . . . . . . 13
⊢ ((𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦) ↔ (𝑥𝐹𝑦 ∧ 𝑥 ∈ 𝐵)) | 
| 11 | 10 | notbii 669 | 
. . . . . . . . . . . 12
⊢ (¬
(𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦) ↔ ¬ (𝑥𝐹𝑦 ∧ 𝑥 ∈ 𝐵)) | 
| 12 |   | imnan 691 | 
. . . . . . . . . . . 12
⊢ ((𝑥𝐹𝑦 → ¬ 𝑥 ∈ 𝐵) ↔ ¬ (𝑥𝐹𝑦 ∧ 𝑥 ∈ 𝐵)) | 
| 13 | 11, 12 | bitr4i 187 | 
. . . . . . . . . . 11
⊢ (¬
(𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦) ↔ (𝑥𝐹𝑦 → ¬ 𝑥 ∈ 𝐵)) | 
| 14 | 9, 13 | sylib 122 | 
. . . . . . . . . 10
⊢ (((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ (𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) → (𝑥𝐹𝑦 → ¬ 𝑥 ∈ 𝐵)) | 
| 15 | 8, 14 | mpd 13 | 
. . . . . . . . 9
⊢ (((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ (𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) → ¬ 𝑥 ∈ 𝐵) | 
| 16 | 7, 15, 8 | jca32 310 | 
. . . . . . . 8
⊢ (((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ (𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) → ((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ (¬ 𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦))) | 
| 17 |   | eldif 3166 | 
. . . . . . . . . 10
⊢ (𝑥 ∈ (𝐴 ∖ 𝐵) ↔ (𝑥 ∈ 𝐴 ∧ ¬ 𝑥 ∈ 𝐵)) | 
| 18 | 17 | anbi1i 458 | 
. . . . . . . . 9
⊢ ((𝑥 ∈ (𝐴 ∖ 𝐵) ∧ 𝑥𝐹𝑦) ↔ ((𝑥 ∈ 𝐴 ∧ ¬ 𝑥 ∈ 𝐵) ∧ 𝑥𝐹𝑦)) | 
| 19 |   | anandir 591 | 
. . . . . . . . 9
⊢ (((𝑥 ∈ 𝐴 ∧ ¬ 𝑥 ∈ 𝐵) ∧ 𝑥𝐹𝑦) ↔ ((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ (¬ 𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦))) | 
| 20 | 18, 19 | bitri 184 | 
. . . . . . . 8
⊢ ((𝑥 ∈ (𝐴 ∖ 𝐵) ∧ 𝑥𝐹𝑦) ↔ ((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ (¬ 𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦))) | 
| 21 | 16, 20 | sylibr 134 | 
. . . . . . 7
⊢ (((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ (𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) → (𝑥 ∈ (𝐴 ∖ 𝐵) ∧ 𝑥𝐹𝑦)) | 
| 22 | 21 | eximi 1614 | 
. . . . . 6
⊢
(∃𝑥((𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ (𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) → ∃𝑥(𝑥 ∈ (𝐴 ∖ 𝐵) ∧ 𝑥𝐹𝑦)) | 
| 23 | 6, 22 | syl 14 | 
. . . . 5
⊢
((∃𝑥(𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ ∃𝑥(𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) → ∃𝑥(𝑥 ∈ (𝐴 ∖ 𝐵) ∧ 𝑥𝐹𝑦)) | 
| 24 |   | df-rex 2481 | 
. . . . 5
⊢
(∃𝑥 ∈
(𝐴 ∖ 𝐵)𝑥𝐹𝑦 ↔ ∃𝑥(𝑥 ∈ (𝐴 ∖ 𝐵) ∧ 𝑥𝐹𝑦)) | 
| 25 | 23, 24 | sylibr 134 | 
. . . 4
⊢
((∃𝑥(𝑥 ∈ 𝐴 ∧ 𝑥𝐹𝑦) ∧ ¬ ∃𝑥(𝑥 ∈ 𝐵 ∧ 𝑥𝐹𝑦)) → ∃𝑥 ∈ (𝐴 ∖ 𝐵)𝑥𝐹𝑦) | 
| 26 | 1, 3, 25 | syl2anb 291 | 
. . 3
⊢
((∃𝑥 ∈
𝐴 𝑥𝐹𝑦 ∧ ¬ ∃𝑥 ∈ 𝐵 𝑥𝐹𝑦) → ∃𝑥 ∈ (𝐴 ∖ 𝐵)𝑥𝐹𝑦) | 
| 27 | 26 | ss2abi 3255 | 
. 2
⊢ {𝑦 ∣ (∃𝑥 ∈ 𝐴 𝑥𝐹𝑦 ∧ ¬ ∃𝑥 ∈ 𝐵 𝑥𝐹𝑦)} ⊆ {𝑦 ∣ ∃𝑥 ∈ (𝐴 ∖ 𝐵)𝑥𝐹𝑦} | 
| 28 |   | dfima2 5011 | 
. . . 4
⊢ (𝐹 “ 𝐴) = {𝑦 ∣ ∃𝑥 ∈ 𝐴 𝑥𝐹𝑦} | 
| 29 |   | dfima2 5011 | 
. . . 4
⊢ (𝐹 “ 𝐵) = {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑥𝐹𝑦} | 
| 30 | 28, 29 | difeq12i 3279 | 
. . 3
⊢ ((𝐹 “ 𝐴) ∖ (𝐹 “ 𝐵)) = ({𝑦 ∣ ∃𝑥 ∈ 𝐴 𝑥𝐹𝑦} ∖ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑥𝐹𝑦}) | 
| 31 |   | difab 3432 | 
. . 3
⊢ ({𝑦 ∣ ∃𝑥 ∈ 𝐴 𝑥𝐹𝑦} ∖ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑥𝐹𝑦}) = {𝑦 ∣ (∃𝑥 ∈ 𝐴 𝑥𝐹𝑦 ∧ ¬ ∃𝑥 ∈ 𝐵 𝑥𝐹𝑦)} | 
| 32 | 30, 31 | eqtri 2217 | 
. 2
⊢ ((𝐹 “ 𝐴) ∖ (𝐹 “ 𝐵)) = {𝑦 ∣ (∃𝑥 ∈ 𝐴 𝑥𝐹𝑦 ∧ ¬ ∃𝑥 ∈ 𝐵 𝑥𝐹𝑦)} | 
| 33 |   | dfima2 5011 | 
. 2
⊢ (𝐹 “ (𝐴 ∖ 𝐵)) = {𝑦 ∣ ∃𝑥 ∈ (𝐴 ∖ 𝐵)𝑥𝐹𝑦} | 
| 34 | 27, 32, 33 | 3sstr4i 3224 | 
1
⊢ ((𝐹 “ 𝐴) ∖ (𝐹 “ 𝐵)) ⊆ (𝐹 “ (𝐴 ∖ 𝐵)) |