In RU (R is the reals, U is the usual topology), prove that any
open interval (a, b) is homeomorphic to the interval (0, 1). (Hint:
construct a function f : (a, b) → (0, 1) for which f(a) = 0 and
f(b) = 1. Show that your map is a homeomorphism by showing that it
is a continuous bijection with a continuous inverse.)