float(zeta(3)) does not evaluate numerically

Alexey has recognized that sign(zeta(x)) does not give the expected
answers when x is a numerical value e. g. sign(zeta(3)) --> 'pnz and not
'pos as expected. (But sign(zeta(3.0)) --> 'pos.)

The reason is that float(zeta(3)) does not evaluate numerically, but
returns float(zeta(3)) --> zeta(3.0).

This is because the function zeta() is a "pure" verb function. There is
no simplifying function implemented.

I do not know any reason why the zeta() function is not implemented as a
simplifying function. But if we would change the implementation to a
simplifying function perhaps we will get the desired and much more
functionality.

Dieter Kaiser