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Definition df-t0 21849
Description: Define T0 or Kolmogorov spaces. A T0 space satisfies a kind of "topological extensionality" principle (compare ax-ext 2790): any two points which are members of the same open sets are equal, or in contraposition, for any two distinct points there is an open set which contains one point but not the other. This differs from T1 spaces (see ist1-2 21883) in that in a T1 space you can choose which point will be in the open set and which outside; in a T0 space you only know that one of the two points is in the set. (Contributed by Jeff Hankins, 1-Feb-2010.)
Assertion
Ref Expression
df-t0 Kol2 = {𝑗 ∈ Top ∣ ∀𝑥 𝑗𝑦 𝑗(∀𝑜𝑗 (𝑥𝑜𝑦𝑜) → 𝑥 = 𝑦)}
Distinct variable group:   𝑗,𝑜,𝑥,𝑦

Detailed syntax breakdown of Definition df-t0
StepHypRef Expression
1 ct0 21842 . 2 class Kol2
2 vx . . . . . . . . 9 setvar 𝑥
3 vo . . . . . . . . 9 setvar 𝑜
42, 3wel 2106 . . . . . . . 8 wff 𝑥𝑜
5 vy . . . . . . . . 9 setvar 𝑦
65, 3wel 2106 . . . . . . . 8 wff 𝑦𝑜
74, 6wb 207 . . . . . . 7 wff (𝑥𝑜𝑦𝑜)
8 vj . . . . . . . 8 setvar 𝑗
98cv 1527 . . . . . . 7 class 𝑗
107, 3, 9wral 3135 . . . . . 6 wff 𝑜𝑗 (𝑥𝑜𝑦𝑜)
112, 5weq 1955 . . . . . 6 wff 𝑥 = 𝑦
1210, 11wi 4 . . . . 5 wff (∀𝑜𝑗 (𝑥𝑜𝑦𝑜) → 𝑥 = 𝑦)
139cuni 4830 . . . . 5 class 𝑗
1412, 5, 13wral 3135 . . . 4 wff 𝑦 𝑗(∀𝑜𝑗 (𝑥𝑜𝑦𝑜) → 𝑥 = 𝑦)
1514, 2, 13wral 3135 . . 3 wff 𝑥 𝑗𝑦 𝑗(∀𝑜𝑗 (𝑥𝑜𝑦𝑜) → 𝑥 = 𝑦)
16 ctop 21429 . . 3 class Top
1715, 8, 16crab 3139 . 2 class {𝑗 ∈ Top ∣ ∀𝑥 𝑗𝑦 𝑗(∀𝑜𝑗 (𝑥𝑜𝑦𝑜) → 𝑥 = 𝑦)}
181, 17wceq 1528 1 wff Kol2 = {𝑗 ∈ Top ∣ ∀𝑥 𝑗𝑦 𝑗(∀𝑜𝑗 (𝑥𝑜𝑦𝑜) → 𝑥 = 𝑦)}
Colors of variables: wff setvar class
This definition is referenced by:  ist0  21856
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