View Compilation Error

0_0_20041014_16222.cpp: In function 'void conv(poly&, poly&, int)':
0_0_20041014_16222.cpp:50:2: error: 'a' is not a class, namespace, or enumeration
  a::FFT(len,1);
  ^
0_0_20041014_16222.cpp:52:2: error: 'res' is not a class, namespace, or enumeration
  res::FFT(len,-1);
  ^