typedef int* ix;
using xi = int*;

int a=10;
const int *ra=&a;
const ix td_a=&a;
const xi us_a=&a;
	
int b=100;
ra=&b;
//*ra=10; *ra read-only
//td_a=&b; td_a read-only 
*td_a=20;
//us_a=&b; us_a read-only 
*us_a=30;