| Step | Hyp | Ref
 | Expression | 
| 1 |   | iooex 9982 | 
. . 3
⊢ (,)
∈ V | 
| 2 | 1 | imaex 5024 | 
. 2
⊢ ((,)
“ (𝑆 × 𝑆)) ∈ V | 
| 3 |   | qtopbas.1 | 
. . . . . . . . 9
⊢ 𝑆 ⊆
ℝ* | 
| 4 | 3 | sseli 3179 | 
. . . . . . . 8
⊢ (𝑧 ∈ 𝑆 → 𝑧 ∈ ℝ*) | 
| 5 | 3 | sseli 3179 | 
. . . . . . . 8
⊢ (𝑤 ∈ 𝑆 → 𝑤 ∈ ℝ*) | 
| 6 | 4, 5 | anim12i 338 | 
. . . . . . 7
⊢ ((𝑧 ∈ 𝑆 ∧ 𝑤 ∈ 𝑆) → (𝑧 ∈ ℝ* ∧ 𝑤 ∈
ℝ*)) | 
| 7 | 3 | sseli 3179 | 
. . . . . . . 8
⊢ (𝑣 ∈ 𝑆 → 𝑣 ∈ ℝ*) | 
| 8 | 3 | sseli 3179 | 
. . . . . . . 8
⊢ (𝑢 ∈ 𝑆 → 𝑢 ∈ ℝ*) | 
| 9 | 7, 8 | anim12i 338 | 
. . . . . . 7
⊢ ((𝑣 ∈ 𝑆 ∧ 𝑢 ∈ 𝑆) → (𝑣 ∈ ℝ* ∧ 𝑢 ∈
ℝ*)) | 
| 10 |   | iooinsup 11442 | 
. . . . . . 7
⊢ (((𝑧 ∈ ℝ*
∧ 𝑤 ∈
ℝ*) ∧ (𝑣 ∈ ℝ* ∧ 𝑢 ∈ ℝ*))
→ ((𝑧(,)𝑤) ∩ (𝑣(,)𝑢)) = (sup({𝑧, 𝑣}, ℝ*, < )(,)inf({𝑤, 𝑢}, ℝ*, <
))) | 
| 11 | 6, 9, 10 | syl2an 289 | 
. . . . . 6
⊢ (((𝑧 ∈ 𝑆 ∧ 𝑤 ∈ 𝑆) ∧ (𝑣 ∈ 𝑆 ∧ 𝑢 ∈ 𝑆)) → ((𝑧(,)𝑤) ∩ (𝑣(,)𝑢)) = (sup({𝑧, 𝑣}, ℝ*, < )(,)inf({𝑤, 𝑢}, ℝ*, <
))) | 
| 12 |   | qtopbas.max | 
. . . . . . . . . . 11
⊢ ((𝑥 ∈ 𝑆 ∧ 𝑦 ∈ 𝑆) → sup({𝑥, 𝑦}, ℝ*, < ) ∈ 𝑆) | 
| 13 | 12 | rgen2a 2551 | 
. . . . . . . . . 10
⊢
∀𝑥 ∈
𝑆 ∀𝑦 ∈ 𝑆 sup({𝑥, 𝑦}, ℝ*, < ) ∈ 𝑆 | 
| 14 |   | preq12 3701 | 
. . . . . . . . . . . . . 14
⊢ ((𝑥 = 𝑣 ∧ 𝑦 = 𝑧) → {𝑥, 𝑦} = {𝑣, 𝑧}) | 
| 15 |   | prcom 3698 | 
. . . . . . . . . . . . . 14
⊢ {𝑣, 𝑧} = {𝑧, 𝑣} | 
| 16 | 14, 15 | eqtrdi 2245 | 
. . . . . . . . . . . . 13
⊢ ((𝑥 = 𝑣 ∧ 𝑦 = 𝑧) → {𝑥, 𝑦} = {𝑧, 𝑣}) | 
| 17 | 16 | supeq1d 7053 | 
. . . . . . . . . . . 12
⊢ ((𝑥 = 𝑣 ∧ 𝑦 = 𝑧) → sup({𝑥, 𝑦}, ℝ*, < ) = sup({𝑧, 𝑣}, ℝ*, <
)) | 
| 18 | 17 | eleq1d 2265 | 
. . . . . . . . . . 11
⊢ ((𝑥 = 𝑣 ∧ 𝑦 = 𝑧) → (sup({𝑥, 𝑦}, ℝ*, < ) ∈ 𝑆 ↔ sup({𝑧, 𝑣}, ℝ*, < ) ∈ 𝑆)) | 
| 19 | 18 | rspc2gv 2880 | 
. . . . . . . . . 10
⊢ ((𝑣 ∈ 𝑆 ∧ 𝑧 ∈ 𝑆) → (∀𝑥 ∈ 𝑆 ∀𝑦 ∈ 𝑆 sup({𝑥, 𝑦}, ℝ*, < ) ∈ 𝑆 → sup({𝑧, 𝑣}, ℝ*, < ) ∈ 𝑆)) | 
| 20 | 13, 19 | mpi 15 | 
. . . . . . . . 9
⊢ ((𝑣 ∈ 𝑆 ∧ 𝑧 ∈ 𝑆) → sup({𝑧, 𝑣}, ℝ*, < ) ∈ 𝑆) | 
| 21 | 20 | ancoms 268 | 
. . . . . . . 8
⊢ ((𝑧 ∈ 𝑆 ∧ 𝑣 ∈ 𝑆) → sup({𝑧, 𝑣}, ℝ*, < ) ∈ 𝑆) | 
| 22 |   | qtopbas.min | 
. . . . . . . . . 10
⊢ ((𝑥 ∈ 𝑆 ∧ 𝑦 ∈ 𝑆) → inf({𝑥, 𝑦}, ℝ*, < ) ∈ 𝑆) | 
| 23 | 22 | rgen2a 2551 | 
. . . . . . . . 9
⊢
∀𝑥 ∈
𝑆 ∀𝑦 ∈ 𝑆 inf({𝑥, 𝑦}, ℝ*, < ) ∈ 𝑆 | 
| 24 |   | preq12 3701 | 
. . . . . . . . . . . 12
⊢ ((𝑥 = 𝑤 ∧ 𝑦 = 𝑢) → {𝑥, 𝑦} = {𝑤, 𝑢}) | 
| 25 | 24 | infeq1d 7078 | 
. . . . . . . . . . 11
⊢ ((𝑥 = 𝑤 ∧ 𝑦 = 𝑢) → inf({𝑥, 𝑦}, ℝ*, < ) = inf({𝑤, 𝑢}, ℝ*, <
)) | 
| 26 | 25 | eleq1d 2265 | 
. . . . . . . . . 10
⊢ ((𝑥 = 𝑤 ∧ 𝑦 = 𝑢) → (inf({𝑥, 𝑦}, ℝ*, < ) ∈ 𝑆 ↔ inf({𝑤, 𝑢}, ℝ*, < ) ∈ 𝑆)) | 
| 27 | 26 | rspc2gv 2880 | 
. . . . . . . . 9
⊢ ((𝑤 ∈ 𝑆 ∧ 𝑢 ∈ 𝑆) → (∀𝑥 ∈ 𝑆 ∀𝑦 ∈ 𝑆 inf({𝑥, 𝑦}, ℝ*, < ) ∈ 𝑆 → inf({𝑤, 𝑢}, ℝ*, < ) ∈ 𝑆)) | 
| 28 | 23, 27 | mpi 15 | 
. . . . . . . 8
⊢ ((𝑤 ∈ 𝑆 ∧ 𝑢 ∈ 𝑆) → inf({𝑤, 𝑢}, ℝ*, < ) ∈ 𝑆) | 
| 29 |   | df-ov 5925 | 
. . . . . . . . 9
⊢
(sup({𝑧, 𝑣}, ℝ*, <
)(,)inf({𝑤, 𝑢}, ℝ*, < ))
= ((,)‘〈sup({𝑧,
𝑣}, ℝ*,
< ), inf({𝑤, 𝑢}, ℝ*, <
)〉) | 
| 30 |   | opelxpi 4695 | 
. . . . . . . . . 10
⊢
((sup({𝑧, 𝑣}, ℝ*, < )
∈ 𝑆 ∧ inf({𝑤, 𝑢}, ℝ*, < ) ∈ 𝑆) → 〈sup({𝑧, 𝑣}, ℝ*, < ), inf({𝑤, 𝑢}, ℝ*, < )〉 ∈
(𝑆 × 𝑆)) | 
| 31 |   | ioof 10046 | 
. . . . . . . . . . . 12
⊢
(,):(ℝ* × ℝ*)⟶𝒫
ℝ | 
| 32 |   | ffun 5410 | 
. . . . . . . . . . . 12
⊢
((,):(ℝ* × ℝ*)⟶𝒫
ℝ → Fun (,)) | 
| 33 | 31, 32 | ax-mp 5 | 
. . . . . . . . . . 11
⊢ Fun
(,) | 
| 34 |   | xpss12 4770 | 
. . . . . . . . . . . . 13
⊢ ((𝑆 ⊆ ℝ*
∧ 𝑆 ⊆
ℝ*) → (𝑆 × 𝑆) ⊆ (ℝ* ×
ℝ*)) | 
| 35 | 3, 3, 34 | mp2an 426 | 
. . . . . . . . . . . 12
⊢ (𝑆 × 𝑆) ⊆ (ℝ* ×
ℝ*) | 
| 36 | 31 | fdmi 5415 | 
. . . . . . . . . . . 12
⊢ dom (,) =
(ℝ* × ℝ*) | 
| 37 | 35, 36 | sseqtrri 3218 | 
. . . . . . . . . . 11
⊢ (𝑆 × 𝑆) ⊆ dom (,) | 
| 38 |   | funfvima2 5795 | 
. . . . . . . . . . 11
⊢ ((Fun (,)
∧ (𝑆 × 𝑆) ⊆ dom (,)) →
(〈sup({𝑧, 𝑣}, ℝ*, < ),
inf({𝑤, 𝑢}, ℝ*, < )〉 ∈
(𝑆 × 𝑆) →
((,)‘〈sup({𝑧,
𝑣}, ℝ*,
< ), inf({𝑤, 𝑢}, ℝ*, <
)〉) ∈ ((,) “ (𝑆 × 𝑆)))) | 
| 39 | 33, 37, 38 | mp2an 426 | 
. . . . . . . . . 10
⊢
(〈sup({𝑧, 𝑣}, ℝ*, < ),
inf({𝑤, 𝑢}, ℝ*, < )〉 ∈
(𝑆 × 𝑆) →
((,)‘〈sup({𝑧,
𝑣}, ℝ*,
< ), inf({𝑤, 𝑢}, ℝ*, <
)〉) ∈ ((,) “ (𝑆 × 𝑆))) | 
| 40 | 30, 39 | syl 14 | 
. . . . . . . . 9
⊢
((sup({𝑧, 𝑣}, ℝ*, < )
∈ 𝑆 ∧ inf({𝑤, 𝑢}, ℝ*, < ) ∈ 𝑆) →
((,)‘〈sup({𝑧,
𝑣}, ℝ*,
< ), inf({𝑤, 𝑢}, ℝ*, <
)〉) ∈ ((,) “ (𝑆 × 𝑆))) | 
| 41 | 29, 40 | eqeltrid 2283 | 
. . . . . . . 8
⊢
((sup({𝑧, 𝑣}, ℝ*, < )
∈ 𝑆 ∧ inf({𝑤, 𝑢}, ℝ*, < ) ∈ 𝑆) → (sup({𝑧, 𝑣}, ℝ*, < )(,)inf({𝑤, 𝑢}, ℝ*, < )) ∈ ((,)
“ (𝑆 × 𝑆))) | 
| 42 | 21, 28, 41 | syl2an 289 | 
. . . . . . 7
⊢ (((𝑧 ∈ 𝑆 ∧ 𝑣 ∈ 𝑆) ∧ (𝑤 ∈ 𝑆 ∧ 𝑢 ∈ 𝑆)) → (sup({𝑧, 𝑣}, ℝ*, < )(,)inf({𝑤, 𝑢}, ℝ*, < )) ∈ ((,)
“ (𝑆 × 𝑆))) | 
| 43 | 42 | an4s 588 | 
. . . . . 6
⊢ (((𝑧 ∈ 𝑆 ∧ 𝑤 ∈ 𝑆) ∧ (𝑣 ∈ 𝑆 ∧ 𝑢 ∈ 𝑆)) → (sup({𝑧, 𝑣}, ℝ*, < )(,)inf({𝑤, 𝑢}, ℝ*, < )) ∈ ((,)
“ (𝑆 × 𝑆))) | 
| 44 | 11, 43 | eqeltrd 2273 | 
. . . . 5
⊢ (((𝑧 ∈ 𝑆 ∧ 𝑤 ∈ 𝑆) ∧ (𝑣 ∈ 𝑆 ∧ 𝑢 ∈ 𝑆)) → ((𝑧(,)𝑤) ∩ (𝑣(,)𝑢)) ∈ ((,) “ (𝑆 × 𝑆))) | 
| 45 | 44 | ralrimivva 2579 | 
. . . 4
⊢ ((𝑧 ∈ 𝑆 ∧ 𝑤 ∈ 𝑆) → ∀𝑣 ∈ 𝑆 ∀𝑢 ∈ 𝑆 ((𝑧(,)𝑤) ∩ (𝑣(,)𝑢)) ∈ ((,) “ (𝑆 × 𝑆))) | 
| 46 | 45 | rgen2a 2551 | 
. . 3
⊢
∀𝑧 ∈
𝑆 ∀𝑤 ∈ 𝑆 ∀𝑣 ∈ 𝑆 ∀𝑢 ∈ 𝑆 ((𝑧(,)𝑤) ∩ (𝑣(,)𝑢)) ∈ ((,) “ (𝑆 × 𝑆)) | 
| 47 |   | ffn 5407 | 
. . . . . 6
⊢
((,):(ℝ* × ℝ*)⟶𝒫
ℝ → (,) Fn (ℝ* ×
ℝ*)) | 
| 48 | 31, 47 | ax-mp 5 | 
. . . . 5
⊢ (,) Fn
(ℝ* × ℝ*) | 
| 49 |   | ineq1 3357 | 
. . . . . . . 8
⊢ (𝑥 = ((,)‘𝑡) → (𝑥 ∩ 𝑦) = (((,)‘𝑡) ∩ 𝑦)) | 
| 50 | 49 | eleq1d 2265 | 
. . . . . . 7
⊢ (𝑥 = ((,)‘𝑡) → ((𝑥 ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ (((,)‘𝑡) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)))) | 
| 51 | 50 | ralbidv 2497 | 
. . . . . 6
⊢ (𝑥 = ((,)‘𝑡) → (∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))(𝑥 ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))(((,)‘𝑡) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)))) | 
| 52 | 51 | ralima 5802 | 
. . . . 5
⊢ (((,) Fn
(ℝ* × ℝ*) ∧ (𝑆 × 𝑆) ⊆ (ℝ* ×
ℝ*)) → (∀𝑥 ∈ ((,) “ (𝑆 × 𝑆))∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))(𝑥 ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ∀𝑡 ∈ (𝑆 × 𝑆)∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))(((,)‘𝑡) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)))) | 
| 53 | 48, 35, 52 | mp2an 426 | 
. . . 4
⊢
(∀𝑥 ∈
((,) “ (𝑆 ×
𝑆))∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))(𝑥 ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ∀𝑡 ∈ (𝑆 × 𝑆)∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))(((,)‘𝑡) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆))) | 
| 54 |   | fveq2 5558 | 
. . . . . . . . . 10
⊢ (𝑡 = 〈𝑧, 𝑤〉 → ((,)‘𝑡) = ((,)‘〈𝑧, 𝑤〉)) | 
| 55 |   | df-ov 5925 | 
. . . . . . . . . 10
⊢ (𝑧(,)𝑤) = ((,)‘〈𝑧, 𝑤〉) | 
| 56 | 54, 55 | eqtr4di 2247 | 
. . . . . . . . 9
⊢ (𝑡 = 〈𝑧, 𝑤〉 → ((,)‘𝑡) = (𝑧(,)𝑤)) | 
| 57 | 56 | ineq1d 3363 | 
. . . . . . . 8
⊢ (𝑡 = 〈𝑧, 𝑤〉 → (((,)‘𝑡) ∩ 𝑦) = ((𝑧(,)𝑤) ∩ 𝑦)) | 
| 58 | 57 | eleq1d 2265 | 
. . . . . . 7
⊢ (𝑡 = 〈𝑧, 𝑤〉 → ((((,)‘𝑡) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ((𝑧(,)𝑤) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)))) | 
| 59 | 58 | ralbidv 2497 | 
. . . . . 6
⊢ (𝑡 = 〈𝑧, 𝑤〉 → (∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))(((,)‘𝑡) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))((𝑧(,)𝑤) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)))) | 
| 60 |   | ineq2 3358 | 
. . . . . . . . . 10
⊢ (𝑦 = ((,)‘𝑡) → ((𝑧(,)𝑤) ∩ 𝑦) = ((𝑧(,)𝑤) ∩ ((,)‘𝑡))) | 
| 61 | 60 | eleq1d 2265 | 
. . . . . . . . 9
⊢ (𝑦 = ((,)‘𝑡) → (((𝑧(,)𝑤) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ((𝑧(,)𝑤) ∩ ((,)‘𝑡)) ∈ ((,) “ (𝑆 × 𝑆)))) | 
| 62 | 61 | ralima 5802 | 
. . . . . . . 8
⊢ (((,) Fn
(ℝ* × ℝ*) ∧ (𝑆 × 𝑆) ⊆ (ℝ* ×
ℝ*)) → (∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))((𝑧(,)𝑤) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ∀𝑡 ∈ (𝑆 × 𝑆)((𝑧(,)𝑤) ∩ ((,)‘𝑡)) ∈ ((,) “ (𝑆 × 𝑆)))) | 
| 63 | 48, 35, 62 | mp2an 426 | 
. . . . . . 7
⊢
(∀𝑦 ∈
((,) “ (𝑆 ×
𝑆))((𝑧(,)𝑤) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ∀𝑡 ∈ (𝑆 × 𝑆)((𝑧(,)𝑤) ∩ ((,)‘𝑡)) ∈ ((,) “ (𝑆 × 𝑆))) | 
| 64 |   | fveq2 5558 | 
. . . . . . . . . . 11
⊢ (𝑡 = 〈𝑣, 𝑢〉 → ((,)‘𝑡) = ((,)‘〈𝑣, 𝑢〉)) | 
| 65 |   | df-ov 5925 | 
. . . . . . . . . . 11
⊢ (𝑣(,)𝑢) = ((,)‘〈𝑣, 𝑢〉) | 
| 66 | 64, 65 | eqtr4di 2247 | 
. . . . . . . . . 10
⊢ (𝑡 = 〈𝑣, 𝑢〉 → ((,)‘𝑡) = (𝑣(,)𝑢)) | 
| 67 | 66 | ineq2d 3364 | 
. . . . . . . . 9
⊢ (𝑡 = 〈𝑣, 𝑢〉 → ((𝑧(,)𝑤) ∩ ((,)‘𝑡)) = ((𝑧(,)𝑤) ∩ (𝑣(,)𝑢))) | 
| 68 | 67 | eleq1d 2265 | 
. . . . . . . 8
⊢ (𝑡 = 〈𝑣, 𝑢〉 → (((𝑧(,)𝑤) ∩ ((,)‘𝑡)) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ((𝑧(,)𝑤) ∩ (𝑣(,)𝑢)) ∈ ((,) “ (𝑆 × 𝑆)))) | 
| 69 | 68 | ralxp 4809 | 
. . . . . . 7
⊢
(∀𝑡 ∈
(𝑆 × 𝑆)((𝑧(,)𝑤) ∩ ((,)‘𝑡)) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ∀𝑣 ∈ 𝑆 ∀𝑢 ∈ 𝑆 ((𝑧(,)𝑤) ∩ (𝑣(,)𝑢)) ∈ ((,) “ (𝑆 × 𝑆))) | 
| 70 | 63, 69 | bitri 184 | 
. . . . . 6
⊢
(∀𝑦 ∈
((,) “ (𝑆 ×
𝑆))((𝑧(,)𝑤) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ∀𝑣 ∈ 𝑆 ∀𝑢 ∈ 𝑆 ((𝑧(,)𝑤) ∩ (𝑣(,)𝑢)) ∈ ((,) “ (𝑆 × 𝑆))) | 
| 71 | 59, 70 | bitrdi 196 | 
. . . . 5
⊢ (𝑡 = 〈𝑧, 𝑤〉 → (∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))(((,)‘𝑡) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ∀𝑣 ∈ 𝑆 ∀𝑢 ∈ 𝑆 ((𝑧(,)𝑤) ∩ (𝑣(,)𝑢)) ∈ ((,) “ (𝑆 × 𝑆)))) | 
| 72 | 71 | ralxp 4809 | 
. . . 4
⊢
(∀𝑡 ∈
(𝑆 × 𝑆)∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))(((,)‘𝑡) ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ∀𝑧 ∈ 𝑆 ∀𝑤 ∈ 𝑆 ∀𝑣 ∈ 𝑆 ∀𝑢 ∈ 𝑆 ((𝑧(,)𝑤) ∩ (𝑣(,)𝑢)) ∈ ((,) “ (𝑆 × 𝑆))) | 
| 73 | 53, 72 | bitri 184 | 
. . 3
⊢
(∀𝑥 ∈
((,) “ (𝑆 ×
𝑆))∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))(𝑥 ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) ↔ ∀𝑧 ∈ 𝑆 ∀𝑤 ∈ 𝑆 ∀𝑣 ∈ 𝑆 ∀𝑢 ∈ 𝑆 ((𝑧(,)𝑤) ∩ (𝑣(,)𝑢)) ∈ ((,) “ (𝑆 × 𝑆))) | 
| 74 | 46, 73 | mpbir 146 | 
. 2
⊢
∀𝑥 ∈
((,) “ (𝑆 ×
𝑆))∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))(𝑥 ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆)) | 
| 75 |   | fiinbas 14285 | 
. 2
⊢ ((((,)
“ (𝑆 × 𝑆)) ∈ V ∧ ∀𝑥 ∈ ((,) “ (𝑆 × 𝑆))∀𝑦 ∈ ((,) “ (𝑆 × 𝑆))(𝑥 ∩ 𝑦) ∈ ((,) “ (𝑆 × 𝑆))) → ((,) “ (𝑆 × 𝑆)) ∈ TopBases) | 
| 76 | 2, 74, 75 | mp2an 426 | 
1
⊢ ((,)
“ (𝑆 × 𝑆)) ∈
TopBases |