cd
ps
ll
whoami
article
academic
G1T1
calculus
0-pre
2-common_logicsym
0-implies_and_iff
iff.md
iff.md
若$A\implies B$且$B\implies A$,则说$A$与$B$
等价
,记为$A\iff B$
例如
数集$E$有界$\iff$$E$既有下界又有上界