这是本文档旧的修订版！

PlayGround

$a$

123	123

don't use codedoc!

#include<bits/c++.h>
 
int main(){
    a ⇐ b;
}

click here if you want to know more

#include<bits/c++.h>
 
int main(){
    a <= b;
}

test

$\empty$ $\emptyset$