What i would like to do is define formal symbolic functions
f1 = function('f1',latex_name = 'f_1')(x)
and set their derivative or at least be able to substitute their derivative. As an example assume I defined f1,f2,f3,f4 then I would set dx f1 = f2+f3 and what I would expect is
f1.derivative(x)
to output
f2(x)+ f3(x)