위상수학 (1) 썸네일형 리스트형 [위상수학] Munkres 12~13 Exercise 풀이 1. 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 $U \subset A$. Show that $A$ is open in $X$. Sol) Let $\mathscr{T}$ is a topology of given set $X$. What we want to show is $A \in \mathscr{T}$. Let $I$ is an index set for open sets $U$ and $\alpha \in I$. By definition of topology, $\bigcup_{\alpha \i.. 이전 1 다음
