Why rearrange?

symbol x("x"); symbol y("y"); symbol a("a"); symbol z("z"); ex e1=a-y+x+z; ex e2=a+x-y+z; cout <<"e1="<< e1 << endl; // e1=a-y+z+x cout <<"e2="<< e2 << endl; // e2=a-y+z+x What if I want to get the same order of the variables which was in expression on creation. How can I do this? And how can I even get ex e3=x+x; cout <<"e3="<< e3 << endl; // e3=x+x ? best regards, Dmitri Gorbenko