Upgrade to access all content for this subject

Which of the following is not a topology on the set $X=\{a,b,c\}$?

Select ALL that apply.

$\tau_1 = \mathcal{P}(X)$

$\tau_2 = \{\{a\}, \{b\}, \{c\}, \{a,b\}, \{a,c\}, \{a,c\}, X\}$

$\tau_3 = \{\emptyset, \{a\}, \{a,b,c\}\}$

$\tau_4 = \{\emptyset, \{a\}, \{b\}, \{a,b,c\}\}$

$\tau_5 = \{\emptyset, \{a,b,c\}\}$