re(a_+b_) := re(a_)+re(b_);
re(a_-b_) := re(a_)-re(b_);
re(a_*b_) := re(a_)*re(b_)-im(a_)*im(b_);
re(Complex(a_,b_)):=a;
re(pi):=pi;
re(x):=x;