/in/foo.cc: In function 'double Length(Vector)':
/in/foo.cc:27:48: error: 'sqrt' was not declared in this scope
 double Length(Vector a) { return sqrt(Dot(a, a)); }
                                                ^
/in/foo.cc: In function 'int dcmp(double)':
/in/foo.cc:34:15: error: 'fabs' was not declared in this scope
     if (fabs(x) < EPS)return 0;
               ^