Topology question
Posted: Fri Sep 11, 2009 4:33 am
I'm reviewing topology from Munkres' 1st book and need some help on exercise (1) on page 83. The question is
Let X be a topological space; let A be a subset of X. Suppose that for each x in A there is an open set U containing x such that U is a subset of A. Show that A is open in X.
Thanks in advance for the help. Also, I'm purchasing his latest book where I can find answers to the exercises on the Internet.
Let X be a topological space; let A be a subset of X. Suppose that for each x in A there is an open set U containing x such that U is a subset of A. Show that A is open in X.
Thanks in advance for the help. Also, I'm purchasing his latest book where I can find answers to the exercises on the Internet.