cd
ps
ll
whoami
article
academic
G1T1
calculus
0-pre
1-func
1-map_and_func
0-map
1-classes
bijection.md
bijection.md
若$f:A\to B$既是
满射
又是
单射
,则称$f$是$A$到$B$的
一一映射
(双射)