pow2(r, int m) >< (int n)
| n == 0 => r~m
| _ => pow2(r, m*2)~(n-1);

pow(r) >< (int n)
| n == 0 => r~1
| _ => pow2(r, 1)~(n);


// Caclulate 2^10
const NUM=10;
pow(r)~NUM; // it can also be written with abbreviation: r << pow(NUM)
r;