Solution

ID: past-exam-of-the-options-ii-course-of-the-university-of-oxford/2009/e/e4/b/ii/solution

If is connected, its continuous quotient image is connected by part (a). Conversely, suppose is disconnected. It has a nonempty proper subset both open and closed. Part (i) makes and its complement saturated, so and . The quotient topology therefore makes these disjoint nonempty images open, and they cover . Thus the quotient is disconnected. This proves the two spaces are connected simultaneously.

New to topics? Read the docs here!