Hi, I try to implement a class for open intervals with interval arithmetic. I followed the instructions written in the GiNaC tutorial (6.5) and also used the implementation of "numeric" etc. as example code in order to get a clue of implementing the operators for my interval class. My goal is to get the class working with GiNaC's term evaluation engine and in particular, allow for polynomials with interval coefficients, which are automatically simplified by the use of the arithmetic operations I implemented. After several trials and errors I implemented a class which should, as I understood GiNaC's structure so far, work as expected - but it does not. I'm now not quite sure what I should concentrate on next or what I misunderstood. Could you give me a hint if it doesn't take you too much time? For further reading I attached, as an example, the open interval class files. I implemented the arithmetic operators in a separate file, just like it is in GiNaC itself. Regards, Ulrich.