View Compilation Error

0_0_35913979_11317.cpp: In function 'long long int qpow(long long int, long long int, long long int)':
0_0_35913979_11317.cpp:49:23: error: 'mul' was not declared in this scope
    sum = mul(sum,a,mod);
                       ^
0_0_35913979_11317.cpp:51:18: error: 'mul' was not declared in this scope
   a = mul(a,a,mod);
                  ^