gp: gdeflate() on power series

[Michael Somos <somos@grail.cba.csuohio.edu>]

pari-dev,

I tried :

? subst(1+x^2+O(x^4),x^2,x)
  ***   incorrect type in gdeflate.

So I wrote :

/* subst(ex,v^n,v) */
{defl(ex,n)=local(v,po,de);
  if(type(ex)==type([]),vector(length(ex),i,defl(ex[i],n)),
   v=variable(ex);po=truncate(ex);de=(valuation(ex,v)+length(Vec(ex)))\n;
   v*O(v^de)+subst(po,v^n,v));
} /* end defl() */

Is it possible to fix 'gdeflate()' so it work on power series?
Also, I used 'valuation(ex,v)+length(Vec(ex))' but I wonder if
there is a better way to get this information in gp. Shalom, Michael