| Step | Hyp | Ref
| Expression |
| 1 | | limord 6418 |
. . . . . . . . . 10
⊢ (Lim
𝐴 → Ord 𝐴) |
| 2 | | ordsson 7782 |
. . . . . . . . . 10
⊢ (Ord
𝐴 → 𝐴 ⊆ On) |
| 3 | | sstr 3972 |
. . . . . . . . . . 11
⊢ ((𝑥 ⊆ 𝐴 ∧ 𝐴 ⊆ On) → 𝑥 ⊆ On) |
| 4 | 3 | expcom 413 |
. . . . . . . . . 10
⊢ (𝐴 ⊆ On → (𝑥 ⊆ 𝐴 → 𝑥 ⊆ On)) |
| 5 | 1, 2, 4 | 3syl 18 |
. . . . . . . . 9
⊢ (Lim
𝐴 → (𝑥 ⊆ 𝐴 → 𝑥 ⊆ On)) |
| 6 | | onsucuni 7827 |
. . . . . . . . 9
⊢ (𝑥 ⊆ On → 𝑥 ⊆ suc ∪ 𝑥) |
| 7 | 5, 6 | syl6 35 |
. . . . . . . 8
⊢ (Lim
𝐴 → (𝑥 ⊆ 𝐴 → 𝑥 ⊆ suc ∪
𝑥)) |
| 8 | 7 | adantrd 491 |
. . . . . . 7
⊢ (Lim
𝐴 → ((𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴)) → 𝑥 ⊆ suc ∪
𝑥)) |
| 9 | 8 | ralimdv 3155 |
. . . . . 6
⊢ (Lim
𝐴 → (∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴)) → ∀𝑥 ∈ 𝐵 𝑥 ⊆ suc ∪
𝑥)) |
| 10 | | uniiun 5039 |
. . . . . . 7
⊢ ∪ 𝐵 =
∪ 𝑥 ∈ 𝐵 𝑥 |
| 11 | | ss2iun 4991 |
. . . . . . 7
⊢
(∀𝑥 ∈
𝐵 𝑥 ⊆ suc ∪
𝑥 → ∪ 𝑥 ∈ 𝐵 𝑥 ⊆ ∪
𝑥 ∈ 𝐵 suc ∪ 𝑥) |
| 12 | 10, 11 | eqsstrid 4002 |
. . . . . 6
⊢
(∀𝑥 ∈
𝐵 𝑥 ⊆ suc ∪
𝑥 → ∪ 𝐵
⊆ ∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥) |
| 13 | 9, 12 | syl6 35 |
. . . . 5
⊢ (Lim
𝐴 → (∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴)) → ∪ 𝐵 ⊆ ∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥)) |
| 14 | 13 | imp 406 |
. . . 4
⊢ ((Lim
𝐴 ∧ ∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴))) → ∪
𝐵 ⊆ ∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥) |
| 15 | | cfslb.1 |
. . . . . . . . . 10
⊢ 𝐴 ∈ V |
| 16 | 15 | cfslbn 10286 |
. . . . . . . . 9
⊢ ((Lim
𝐴 ∧ 𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴)) → ∪ 𝑥 ∈ 𝐴) |
| 17 | 16 | 3expib 1122 |
. . . . . . . 8
⊢ (Lim
𝐴 → ((𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴)) → ∪ 𝑥 ∈ 𝐴)) |
| 18 | | ordsucss 7817 |
. . . . . . . 8
⊢ (Ord
𝐴 → (∪ 𝑥
∈ 𝐴 → suc ∪ 𝑥
⊆ 𝐴)) |
| 19 | 1, 17, 18 | sylsyld 61 |
. . . . . . 7
⊢ (Lim
𝐴 → ((𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴)) → suc ∪
𝑥 ⊆ 𝐴)) |
| 20 | 19 | ralimdv 3155 |
. . . . . 6
⊢ (Lim
𝐴 → (∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴)) → ∀𝑥 ∈ 𝐵 suc ∪ 𝑥 ⊆ 𝐴)) |
| 21 | | iunss 5026 |
. . . . . 6
⊢ (∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 ⊆ 𝐴 ↔ ∀𝑥 ∈ 𝐵 suc ∪ 𝑥 ⊆ 𝐴) |
| 22 | 20, 21 | imbitrrdi 252 |
. . . . 5
⊢ (Lim
𝐴 → (∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴)) → ∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 ⊆ 𝐴)) |
| 23 | 22 | imp 406 |
. . . 4
⊢ ((Lim
𝐴 ∧ ∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴))) → ∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 ⊆ 𝐴) |
| 24 | | sseq1 3989 |
. . . . . 6
⊢ (∪ 𝐵 =
𝐴 → (∪ 𝐵
⊆ ∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 ↔ 𝐴 ⊆ ∪
𝑥 ∈ 𝐵 suc ∪ 𝑥)) |
| 25 | | eqss 3979 |
. . . . . . 7
⊢ (∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 = 𝐴 ↔ (∪
𝑥 ∈ 𝐵 suc ∪ 𝑥 ⊆ 𝐴 ∧ 𝐴 ⊆ ∪
𝑥 ∈ 𝐵 suc ∪ 𝑥)) |
| 26 | 25 | simplbi2com 502 |
. . . . . 6
⊢ (𝐴 ⊆ ∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 → (∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 ⊆ 𝐴 → ∪
𝑥 ∈ 𝐵 suc ∪ 𝑥 = 𝐴)) |
| 27 | 24, 26 | biimtrdi 253 |
. . . . 5
⊢ (∪ 𝐵 =
𝐴 → (∪ 𝐵
⊆ ∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 → (∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 ⊆ 𝐴 → ∪
𝑥 ∈ 𝐵 suc ∪ 𝑥 = 𝐴))) |
| 28 | 27 | com3l 89 |
. . . 4
⊢ (∪ 𝐵
⊆ ∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 → (∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 ⊆ 𝐴 → (∪ 𝐵 = 𝐴 → ∪
𝑥 ∈ 𝐵 suc ∪ 𝑥 = 𝐴))) |
| 29 | 14, 23, 28 | sylc 65 |
. . 3
⊢ ((Lim
𝐴 ∧ ∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴))) → (∪
𝐵 = 𝐴 → ∪
𝑥 ∈ 𝐵 suc ∪ 𝑥 = 𝐴)) |
| 30 | | limsuc 7849 |
. . . . . . . . 9
⊢ (Lim
𝐴 → (∪ 𝑥
∈ 𝐴 ↔ suc ∪ 𝑥
∈ 𝐴)) |
| 31 | 17, 30 | sylibd 239 |
. . . . . . . 8
⊢ (Lim
𝐴 → ((𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴)) → suc ∪
𝑥 ∈ 𝐴)) |
| 32 | 31 | ralimdv 3155 |
. . . . . . 7
⊢ (Lim
𝐴 → (∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴)) → ∀𝑥 ∈ 𝐵 suc ∪ 𝑥 ∈ 𝐴)) |
| 33 | 32 | imp 406 |
. . . . . 6
⊢ ((Lim
𝐴 ∧ ∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴))) → ∀𝑥 ∈ 𝐵 suc ∪ 𝑥 ∈ 𝐴) |
| 34 | | r19.29 3102 |
. . . . . . . 8
⊢
((∀𝑥 ∈
𝐵 suc ∪ 𝑥
∈ 𝐴 ∧ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥) → ∃𝑥 ∈ 𝐵 (suc ∪ 𝑥 ∈ 𝐴 ∧ 𝑦 = suc ∪ 𝑥)) |
| 35 | | eleq1 2823 |
. . . . . . . . . 10
⊢ (𝑦 = suc ∪ 𝑥
→ (𝑦 ∈ 𝐴 ↔ suc ∪ 𝑥
∈ 𝐴)) |
| 36 | 35 | biimparc 479 |
. . . . . . . . 9
⊢ ((suc
∪ 𝑥 ∈ 𝐴 ∧ 𝑦 = suc ∪ 𝑥) → 𝑦 ∈ 𝐴) |
| 37 | 36 | rexlimivw 3138 |
. . . . . . . 8
⊢
(∃𝑥 ∈
𝐵 (suc ∪ 𝑥
∈ 𝐴 ∧ 𝑦 = suc ∪ 𝑥)
→ 𝑦 ∈ 𝐴) |
| 38 | 34, 37 | syl 17 |
. . . . . . 7
⊢
((∀𝑥 ∈
𝐵 suc ∪ 𝑥
∈ 𝐴 ∧ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥) → 𝑦 ∈ 𝐴) |
| 39 | 38 | ex 412 |
. . . . . 6
⊢
(∀𝑥 ∈
𝐵 suc ∪ 𝑥
∈ 𝐴 →
(∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥 → 𝑦 ∈ 𝐴)) |
| 40 | 33, 39 | syl 17 |
. . . . 5
⊢ ((Lim
𝐴 ∧ ∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴))) → (∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥 → 𝑦 ∈ 𝐴)) |
| 41 | 40 | abssdv 4048 |
. . . 4
⊢ ((Lim
𝐴 ∧ ∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴))) → {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} ⊆ 𝐴) |
| 42 | | vuniex 7738 |
. . . . . . . 8
⊢ ∪ 𝑥
∈ V |
| 43 | 42 | sucex 7805 |
. . . . . . 7
⊢ suc ∪ 𝑥
∈ V |
| 44 | 43 | dfiun2 5014 |
. . . . . 6
⊢ ∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 = ∪
{𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} |
| 45 | 44 | eqeq1i 2741 |
. . . . 5
⊢ (∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 = 𝐴 ↔ ∪ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} = 𝐴) |
| 46 | 15 | cfslb 10285 |
. . . . . 6
⊢ ((Lim
𝐴 ∧ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} ⊆ 𝐴 ∧ ∪ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} = 𝐴) → (cf‘𝐴) ≼ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥}) |
| 47 | 46 | 3expia 1121 |
. . . . 5
⊢ ((Lim
𝐴 ∧ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} ⊆ 𝐴) → (∪
{𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} = 𝐴 → (cf‘𝐴) ≼ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥})) |
| 48 | 45, 47 | biimtrid 242 |
. . . 4
⊢ ((Lim
𝐴 ∧ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} ⊆ 𝐴) → (∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 = 𝐴 → (cf‘𝐴) ≼ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥})) |
| 49 | 41, 48 | syldan 591 |
. . 3
⊢ ((Lim
𝐴 ∧ ∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴))) → (∪ 𝑥 ∈ 𝐵 suc ∪ 𝑥 = 𝐴 → (cf‘𝐴) ≼ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥})) |
| 50 | | eqid 2736 |
. . . . . . . . 9
⊢ (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) = (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) |
| 51 | 50 | rnmpt 5942 |
. . . . . . . 8
⊢ ran
(𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) = {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} |
| 52 | 43, 50 | fnmpti 6686 |
. . . . . . . . . 10
⊢ (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) Fn 𝐵 |
| 53 | | dffn4 6801 |
. . . . . . . . . 10
⊢ ((𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) Fn 𝐵 ↔ (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥):𝐵–onto→ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥)) |
| 54 | 52, 53 | mpbi 230 |
. . . . . . . . 9
⊢ (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥):𝐵–onto→ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) |
| 55 | | relsdom 8971 |
. . . . . . . . . . 11
⊢ Rel
≺ |
| 56 | 55 | brrelex1i 5715 |
. . . . . . . . . 10
⊢ (𝐵 ≺ (cf‘𝐴) → 𝐵 ∈ V) |
| 57 | | breq1 5127 |
. . . . . . . . . . . 12
⊢ (𝑦 = 𝐵 → (𝑦 ≺ (cf‘𝐴) ↔ 𝐵 ≺ (cf‘𝐴))) |
| 58 | | foeq2 6792 |
. . . . . . . . . . . . 13
⊢ (𝑦 = 𝐵 → ((𝑥 ∈ 𝐵 ↦ suc ∪
𝑥):𝑦–onto→ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) ↔ (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥):𝐵–onto→ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥))) |
| 59 | | breq2 5128 |
. . . . . . . . . . . . 13
⊢ (𝑦 = 𝐵 → (ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) ≼ 𝑦 ↔ ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) ≼ 𝐵)) |
| 60 | 58, 59 | imbi12d 344 |
. . . . . . . . . . . 12
⊢ (𝑦 = 𝐵 → (((𝑥 ∈ 𝐵 ↦ suc ∪
𝑥):𝑦–onto→ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) → ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) ≼ 𝑦) ↔ ((𝑥 ∈ 𝐵 ↦ suc ∪
𝑥):𝐵–onto→ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) → ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) ≼ 𝐵))) |
| 61 | 57, 60 | imbi12d 344 |
. . . . . . . . . . 11
⊢ (𝑦 = 𝐵 → ((𝑦 ≺ (cf‘𝐴) → ((𝑥 ∈ 𝐵 ↦ suc ∪
𝑥):𝑦–onto→ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) → ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) ≼ 𝑦)) ↔ (𝐵 ≺ (cf‘𝐴) → ((𝑥 ∈ 𝐵 ↦ suc ∪
𝑥):𝐵–onto→ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) → ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) ≼ 𝐵)))) |
| 62 | | cfon 10274 |
. . . . . . . . . . . . 13
⊢
(cf‘𝐴) ∈
On |
| 63 | | sdomdom 8999 |
. . . . . . . . . . . . 13
⊢ (𝑦 ≺ (cf‘𝐴) → 𝑦 ≼ (cf‘𝐴)) |
| 64 | | ondomen 10056 |
. . . . . . . . . . . . 13
⊢
(((cf‘𝐴)
∈ On ∧ 𝑦 ≼
(cf‘𝐴)) → 𝑦 ∈ dom
card) |
| 65 | 62, 63, 64 | sylancr 587 |
. . . . . . . . . . . 12
⊢ (𝑦 ≺ (cf‘𝐴) → 𝑦 ∈ dom card) |
| 66 | | fodomnum 10076 |
. . . . . . . . . . . 12
⊢ (𝑦 ∈ dom card → ((𝑥 ∈ 𝐵 ↦ suc ∪
𝑥):𝑦–onto→ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) → ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) ≼ 𝑦)) |
| 67 | 65, 66 | syl 17 |
. . . . . . . . . . 11
⊢ (𝑦 ≺ (cf‘𝐴) → ((𝑥 ∈ 𝐵 ↦ suc ∪
𝑥):𝑦–onto→ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) → ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) ≼ 𝑦)) |
| 68 | 61, 67 | vtoclg 3538 |
. . . . . . . . . 10
⊢ (𝐵 ∈ V → (𝐵 ≺ (cf‘𝐴) → ((𝑥 ∈ 𝐵 ↦ suc ∪
𝑥):𝐵–onto→ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) → ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) ≼ 𝐵))) |
| 69 | 56, 68 | mpcom 38 |
. . . . . . . . 9
⊢ (𝐵 ≺ (cf‘𝐴) → ((𝑥 ∈ 𝐵 ↦ suc ∪
𝑥):𝐵–onto→ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) → ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) ≼ 𝐵)) |
| 70 | 54, 69 | mpi 20 |
. . . . . . . 8
⊢ (𝐵 ≺ (cf‘𝐴) → ran (𝑥 ∈ 𝐵 ↦ suc ∪
𝑥) ≼ 𝐵) |
| 71 | 51, 70 | eqbrtrrid 5160 |
. . . . . . 7
⊢ (𝐵 ≺ (cf‘𝐴) → {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} ≼ 𝐵) |
| 72 | | domtr 9026 |
. . . . . . 7
⊢
(((cf‘𝐴)
≼ {𝑦 ∣
∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} ∧ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} ≼ 𝐵) → (cf‘𝐴) ≼ 𝐵) |
| 73 | 71, 72 | sylan2 593 |
. . . . . 6
⊢
(((cf‘𝐴)
≼ {𝑦 ∣
∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} ∧ 𝐵 ≺ (cf‘𝐴)) → (cf‘𝐴) ≼ 𝐵) |
| 74 | | domnsym 9118 |
. . . . . 6
⊢
((cf‘𝐴)
≼ 𝐵 → ¬
𝐵 ≺ (cf‘𝐴)) |
| 75 | 73, 74 | syl 17 |
. . . . 5
⊢
(((cf‘𝐴)
≼ {𝑦 ∣
∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} ∧ 𝐵 ≺ (cf‘𝐴)) → ¬ 𝐵 ≺ (cf‘𝐴)) |
| 76 | 75 | pm2.01da 798 |
. . . 4
⊢
((cf‘𝐴)
≼ {𝑦 ∣
∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} → ¬ 𝐵 ≺ (cf‘𝐴)) |
| 77 | 76 | a1i 11 |
. . 3
⊢ ((Lim
𝐴 ∧ ∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴))) → ((cf‘𝐴) ≼ {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 = suc ∪ 𝑥} → ¬ 𝐵 ≺ (cf‘𝐴))) |
| 78 | 29, 49, 77 | 3syld 60 |
. 2
⊢ ((Lim
𝐴 ∧ ∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴))) → (∪
𝐵 = 𝐴 → ¬ 𝐵 ≺ (cf‘𝐴))) |
| 79 | 78 | necon2ad 2948 |
1
⊢ ((Lim
𝐴 ∧ ∀𝑥 ∈ 𝐵 (𝑥 ⊆ 𝐴 ∧ 𝑥 ≺ (cf‘𝐴))) → (𝐵 ≺ (cf‘𝐴) → ∪ 𝐵 ≠ 𝐴)) |