[GiNaC-list] Tutorial: Sub Class from symbol mysymbol.cpp

As today everybody "googles" to find quick answer, I think this example will be usefull to somebody like me, starting making clases with GiNaC. This is a modified versions of Alexei's reply: "Re: Defining a new symbol class (mysymbol.cpp)" The new mysymbol class provides total time derivative. The numbering corresponds to the steps of the mystring Tutorial at Ginacs Tutorial. It works with GiNaC 1.3.6 & 1.4 Enjoy, and thanks again Javier