$\phi$  

{a}

{b}

X

 $\phi$  

X

None  of these

both above

 $\tau=\left\{\phi,\left\{a\right\}\right\}$  

 $\tau=\left\{\phi,X\right\}$  

 $\tau=\left\{\phi,\left\{a\right\},X\right\}$  

 $\tau=\left\{\phi,\left\{a\right\},\left\{b\right\},X\right\}$  

Trivial topology

Discrete topology

non trivial

non discrete

C L Chang

D.Coker

J. C. Kelly

S.Chandrasekar

S.Chandrasekar

A.S.Mashhour

T.R.Hamlett

Muhammad Shabir