L4_A
2.3 Closed set (end.)
2.4 Accumalation points
(1)definition
L4_B
2.4 Accumalation points(cont.)
2.4 Accumalation points(cont.)
(1)Thm for accumulation points
(2)in finite set (in a metric space)
L4_C
2.4 Accumalation points(cont.)
2.4 Accumalation points(cont.)
(1)in infinite set
(2)in R (of one,two dimension)
L4_D
2.4 Accumalation points(end.)
2.4 Accumalation points(end.)
(1)for 交集,聯集,包含
(2)A is closed if and only if A'⊂A.