[GiNaC-list] Problem in adding functions

Hi, I was trying to add some functions (e.g. binary xor) to the Ginac expressions as it is done for functions like cos. The library is accepting those functions standalone but not using them with any coefficients. e.g. it is giving me expressions like XOR(e1, e2) but not like c*XOR(e1, e2) where c is a constant. Could someone point me to the place in library where it scales the functions by multiplying with some constants. Thanks, Nikhil