[GiNaC-list] indexed

Hi, I'm new to ginac, I'd like to know if is it possible to unroll indexed objects. As example, I would like to do something like this a_i a~i = (a_1)^2 + (a_2)^2 + (a_3)^2 + ... or just substituting a_i values in a_i * b~i a_i = =(1,0,0) a_i b~i -> b~1 Thanks a lot for your work.