HI I've got this question I don't know how to do;
Let X be a metric space, and let Q,J be non-empty subsets of X. prove that
inf{dist(x,J):x is a member of Q}= inf{dist(Q,y):y is a member of J}.
I know that the dist(x,J):= inf{d(x,y)|y is a member of J}, I thought maybe if I tried to...