In: Advanced Math
Let X = NN endowed with the product topology. For x ∈ X denote x by (x1, x2, x3, . . .).
(a) Decide if the function given by d : X × X → R is a metric on X where, d(x, x) = 0 and if x is not equal to y then d(x, y) = 1/n where n is the least value for which xn is not equal to yn. Prove your answer.
(b) Show that no compact set in X can contain a non-empty open set.