Currently, symbolic expressions are managed by Ginac which works very well. But for some reasons (as GPL license, cln portage, modern c++ ), it will be interesting to support other backends with seamless use.

It will be nice to implement this backend structure in feel++ and support (in addition to Ginac) :

• SymEngine : is a standalone fast C++ symbolic manipulation library. Codes are quite modern and quite easy to use. It's the same developers of SymPy and will be the backend of SymPy.
• SymPy python library for symbolic mathematics. SymPy will be slower than C++ backend but offers many interesting features.