unique expressions

How can I make an expresion unique? That is, I want it to copy the thing it references not just increment the reference. I envision something like the following pseudocode: symbol x("x"); ex a = pow(x,2)+2*x+1; ex b = a; // make b reference the same thing as a b.make_unique(); // make a new copy of a and reference it with b. Thanks. -- Ben Sapp Los Alamos National Laboratory email: <mailto:bsapp@lanl.gov> Phone: (505)667-3277 Fax: (505)665-7920 URL: http://www.neutrino.lanl.gov/ -- - To UNSUBSCRIBE, email to ginac-list@ginac.de with a subject of "unsubscribe".