[GAP Forum] does a multivariate polynomial know its ring (or at least variables)?

[dmitrii.pasechnik at cs.ox.ac.uk]

Dear all,

I'd like to write a function that takes a multivariate polynomial p
and produces another polynomial in the same polynomial ring R,
by doing a variable subsitution.

Is there a way to p about its ring,
or at least about the family of the indeterminants of the ring?
Namely, I'd like to call
Value( p, vars, vals ), something like
the following:

  # compute the image of q under a linear transform g
  n := Length(vars);
  OnPoly:=function(q,g)
    local i,j;
    return Value(q, vars,
        List([1..n],i->Sum([1..n], j->g[i][j]*vars[j])));
    end;

but I would rather get vars from q.
Have I missed something in the docs?

Thanks,
Dima