Hi, can one help me please;

For S=(0,1)

We know the Cauchy sequences Xn=1/n converges to zero which is not in the set

and Xn=1/n+1 converges to one which is also not in the set

so S=[0,1].

For S= [0,1] n {Rational numbers}

is it just the set of all Real numbers.

For S={1/k:k=1,2,3,...}

Not really to sure about this one

Many thanks