Dear Aaron, your suggestion did work, HOWEVER i had to upgrade sympy to 1.0. It did nothing on 0.7.6 (the default one on ubuntu 16.04)
only writing here to "document" this behaviour regards Riccardo -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sympy+unsubscr...@googlegroups.com. To post to this group, send email to email@example.com. Visit this group at https://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/8817f5c7-cf92-46ba-8a4d-d1e9d2a1484c%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.