Getting the variable of a polynomial

[Jeroen Demeyer <jdemeyer@cage.ugent.be>]

Hi all,

Is there a way in GP to get the variable of a polynomial?  Something 
like polvar(t^2 + t - 5) which would return t.  It would be very useful 
to make polynomials (say, using Pol()) having the same variable as a 
given polynomial.

I checked the documentation, but could not find it.

Jeroen