Hi, Jan!

the GiNaC info documentation claims:

Both symbols and user-defined functions can be specified as being non-commutative.

I couldn't figure out how to create a non-commutative symbol, though, except by defining a new subclass of symbol and overloading return_type()

This is the correct (and at the moment the only) way to create a non-commutative symbol. Best regards, Alexei