| Step | Hyp | Ref
 | Expression | 
| 1 |   | rdgss.5 | 
. . . 4
⊢ (𝜑 → 𝐴 ⊆ 𝐵) | 
| 2 |   | ssel 3177 | 
. . . . . 6
⊢ (𝐴 ⊆ 𝐵 → (𝑥 ∈ 𝐴 → 𝑥 ∈ 𝐵)) | 
| 3 |   | ssid 3203 | 
. . . . . . 7
⊢ (𝐹‘(rec(𝐹, 𝐼)‘𝑥)) ⊆ (𝐹‘(rec(𝐹, 𝐼)‘𝑥)) | 
| 4 |   | fveq2 5558 | 
. . . . . . . . . 10
⊢ (𝑦 = 𝑥 → (rec(𝐹, 𝐼)‘𝑦) = (rec(𝐹, 𝐼)‘𝑥)) | 
| 5 | 4 | fveq2d 5562 | 
. . . . . . . . 9
⊢ (𝑦 = 𝑥 → (𝐹‘(rec(𝐹, 𝐼)‘𝑦)) = (𝐹‘(rec(𝐹, 𝐼)‘𝑥))) | 
| 6 | 5 | sseq2d 3213 | 
. . . . . . . 8
⊢ (𝑦 = 𝑥 → ((𝐹‘(rec(𝐹, 𝐼)‘𝑥)) ⊆ (𝐹‘(rec(𝐹, 𝐼)‘𝑦)) ↔ (𝐹‘(rec(𝐹, 𝐼)‘𝑥)) ⊆ (𝐹‘(rec(𝐹, 𝐼)‘𝑥)))) | 
| 7 | 6 | rspcev 2868 | 
. . . . . . 7
⊢ ((𝑥 ∈ 𝐵 ∧ (𝐹‘(rec(𝐹, 𝐼)‘𝑥)) ⊆ (𝐹‘(rec(𝐹, 𝐼)‘𝑥))) → ∃𝑦 ∈ 𝐵 (𝐹‘(rec(𝐹, 𝐼)‘𝑥)) ⊆ (𝐹‘(rec(𝐹, 𝐼)‘𝑦))) | 
| 8 | 3, 7 | mpan2 425 | 
. . . . . 6
⊢ (𝑥 ∈ 𝐵 → ∃𝑦 ∈ 𝐵 (𝐹‘(rec(𝐹, 𝐼)‘𝑥)) ⊆ (𝐹‘(rec(𝐹, 𝐼)‘𝑦))) | 
| 9 | 2, 8 | syl6 33 | 
. . . . 5
⊢ (𝐴 ⊆ 𝐵 → (𝑥 ∈ 𝐴 → ∃𝑦 ∈ 𝐵 (𝐹‘(rec(𝐹, 𝐼)‘𝑥)) ⊆ (𝐹‘(rec(𝐹, 𝐼)‘𝑦)))) | 
| 10 | 9 | ralrimiv 2569 | 
. . . 4
⊢ (𝐴 ⊆ 𝐵 → ∀𝑥 ∈ 𝐴 ∃𝑦 ∈ 𝐵 (𝐹‘(rec(𝐹, 𝐼)‘𝑥)) ⊆ (𝐹‘(rec(𝐹, 𝐼)‘𝑦))) | 
| 11 | 1, 10 | syl 14 | 
. . 3
⊢ (𝜑 → ∀𝑥 ∈ 𝐴 ∃𝑦 ∈ 𝐵 (𝐹‘(rec(𝐹, 𝐼)‘𝑥)) ⊆ (𝐹‘(rec(𝐹, 𝐼)‘𝑦))) | 
| 12 |   | iunss2 3961 | 
. . 3
⊢
(∀𝑥 ∈
𝐴 ∃𝑦 ∈ 𝐵 (𝐹‘(rec(𝐹, 𝐼)‘𝑥)) ⊆ (𝐹‘(rec(𝐹, 𝐼)‘𝑦)) → ∪
𝑥 ∈ 𝐴 (𝐹‘(rec(𝐹, 𝐼)‘𝑥)) ⊆ ∪ 𝑦 ∈ 𝐵 (𝐹‘(rec(𝐹, 𝐼)‘𝑦))) | 
| 13 |   | unss2 3334 | 
. . 3
⊢ (∪ 𝑥 ∈ 𝐴 (𝐹‘(rec(𝐹, 𝐼)‘𝑥)) ⊆ ∪ 𝑦 ∈ 𝐵 (𝐹‘(rec(𝐹, 𝐼)‘𝑦)) → (𝐼 ∪ ∪
𝑥 ∈ 𝐴 (𝐹‘(rec(𝐹, 𝐼)‘𝑥))) ⊆ (𝐼 ∪ ∪
𝑦 ∈ 𝐵 (𝐹‘(rec(𝐹, 𝐼)‘𝑦)))) | 
| 14 | 11, 12, 13 | 3syl 17 | 
. 2
⊢ (𝜑 → (𝐼 ∪ ∪
𝑥 ∈ 𝐴 (𝐹‘(rec(𝐹, 𝐼)‘𝑥))) ⊆ (𝐼 ∪ ∪
𝑦 ∈ 𝐵 (𝐹‘(rec(𝐹, 𝐼)‘𝑦)))) | 
| 15 |   | rdgss.1 | 
. . 3
⊢ (𝜑 → 𝐹 Fn V) | 
| 16 |   | rdgss.2 | 
. . 3
⊢ (𝜑 → 𝐼 ∈ 𝑉) | 
| 17 |   | rdgss.3 | 
. . 3
⊢ (𝜑 → 𝐴 ∈ On) | 
| 18 |   | rdgival 6440 | 
. . 3
⊢ ((𝐹 Fn V ∧ 𝐼 ∈ 𝑉 ∧ 𝐴 ∈ On) → (rec(𝐹, 𝐼)‘𝐴) = (𝐼 ∪ ∪
𝑥 ∈ 𝐴 (𝐹‘(rec(𝐹, 𝐼)‘𝑥)))) | 
| 19 | 15, 16, 17, 18 | syl3anc 1249 | 
. 2
⊢ (𝜑 → (rec(𝐹, 𝐼)‘𝐴) = (𝐼 ∪ ∪
𝑥 ∈ 𝐴 (𝐹‘(rec(𝐹, 𝐼)‘𝑥)))) | 
| 20 |   | rdgss.4 | 
. . 3
⊢ (𝜑 → 𝐵 ∈ On) | 
| 21 |   | rdgival 6440 | 
. . 3
⊢ ((𝐹 Fn V ∧ 𝐼 ∈ 𝑉 ∧ 𝐵 ∈ On) → (rec(𝐹, 𝐼)‘𝐵) = (𝐼 ∪ ∪
𝑦 ∈ 𝐵 (𝐹‘(rec(𝐹, 𝐼)‘𝑦)))) | 
| 22 | 15, 16, 20, 21 | syl3anc 1249 | 
. 2
⊢ (𝜑 → (rec(𝐹, 𝐼)‘𝐵) = (𝐼 ∪ ∪
𝑦 ∈ 𝐵 (𝐹‘(rec(𝐹, 𝐼)‘𝑦)))) | 
| 23 | 14, 19, 22 | 3sstr4d 3228 | 
1
⊢ (𝜑 → (rec(𝐹, 𝐼)‘𝐴) ⊆ (rec(𝐹, 𝐼)‘𝐵)) |