}
V_3d V_3d:: operator =(V_3d t)
{
x=t.x; y=t.y; z=t.z;
return *this;
ostream &operator <<(ostream &stream,V_3d t)
stream<<"x="<<t.x<<",";
stream<<"y="<<t.y<<",";
stream<<"z="<<t.z<<"n";