Function: poldegree
Section: polynomials
C-Name: poldegree
Prototype: lGDn
Help: poldegree(x,{v}): degree of the polynomial or rational function x with
 respect to main variable if v is omitted, with respect to v otherwise.
 For scalar x, return 0 is x is non-zero and a negative number otherwise.
Description:
 (pol):small                degpol($1)
 (gen):small                degree($1)
 (gen, var):small           poldegree($1, $2)
Doc: degree of the polynomial $x$ in the main variable if $v$ is omitted, in
 the variable $v$ otherwise.

 The degree of $0$ is a fixed negative number, whose exact value should not
 be used. The degree of a non-zero scalar is $0$. Finally, when $x$ is a
 non-zero polynomial or rational function, returns the ordinary degree of
 $x$. Raise an error otherwise.