[CAS] PART FUNCTION on sum of n terms

[parisse]

Correct. That's precisely because I knew the limitations of having binary + and * that I designed Giac with n-ary + and *. One of the limitation (that is perhaps not obvious on a calc) is to be able to handle sums with a very large number of arguments (for example 1 million). With binary + the last argument would be so much embedded that many symbolic operations would segfault because of stack overflow during recursion.