[GiNaC-list] How can I build an expression one character at a time?

Hi guys, I recently started using ginac, and one thing I couldnt figure out from the tutorial is how can I make an expression one piece at a time. So if I wanted to build an expresison out of a list like x,=,5,*,4 I imagine doing something like ex expr; expr.append(x); expr.append(==); expr.append(5); expr.append(4); I understand the numbers are numerics, and x would be a symbol, but I dont know what the operators would be ( * / + - ). Does anyone how I can do this? Does this even make any sense to you? Thanks for any replies! R. Gordon