定理2.4.1设X是一个拓扑空间,则 (1)d(φ)=中 (2)若AcB,则d(A)cd(B) (3)d(AUB)=d(A)d(B) (4)d(d(A))Ad(A)定理2.4.1 设 X 是一个拓扑空间,则 (1) (2) 若 ,则 (3) (4) d( ) = A B d A d B ( ) ( ) d A B d A d B ( ) ( ) ( ) = d d A A d A ( ( )) ( ) 定理2.4.1 设 X 是一个拓扑空间,则 (1) (2) 若 ,则 (3) (4) d( ) = A B d A d B ( ) ( ) d A B d A d B ( ) ( ) ( ) = d d A A d A ( ( )) ( ) 定理2.4.1 设 X 是一个拓扑空间,则 (1) (2) 若 ,则 (3) (4) d( ) = A B d A d B ( ) ( ) d A B d A d B ( ) ( ) ( ) = d d A A d A ( ( )) ( ) 定理2.4.1 设 X 是一个拓扑空间,则 (1) (2) 若 ,则 (3) (4) d( ) = A B d A d B ( ) ( ) d A B d A d B ( ) ( ) ( ) = d d A A d A ( ( )) ( ) 定理2.4.1 设 X 是一个拓扑空间,则 (1) (2) 若 ,则 (3) (4) d( ) = A B d A d B ( ) ( ) d A B d A d B ( ) ( ) ( ) = d d A A d A ( ( )) ( )