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waht
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This is a problem 1 from Munkres pg 83. I'm trying to solve for self study.
Let X be a topological space; let A be a subset of X. Suppose that for each x belonging 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.
I'm not sure exactly how an open subset of A makes the whole A open.
Thanks
Let X be a topological space; let A be a subset of X. Suppose that for each x belonging 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.
I'm not sure exactly how an open subset of A makes the whole A open.
Thanks