2楼: Originally posted by hank612 at 2013-08-02 00:18:34
for example,
X={1}, Y={2,3},
f: X->Y by f(1)=2, and g: Y-> X by g(2)=g(3)=1.  
Then f is mono and g is epi.
but f(X) != Y.

画圈的地方, 准确来说应该是 '包含或等于', 就是下面还有短横线的 ...

3楼: Originally posted by f867 at 2013-08-02 00:35:02
谢谢您的回复：
但是有个小问题：EPI是什么意思？？
谢谢。...