intrinsic HeckeOperator(f::RngSerPuisElt, ell::RngIntElt) -> RngSerElt
{Compute T_ell(f).}
   require IsPrime(ell) : "Argument 2 must be prime.";
 
   R<q> := Parent(f);
   prec := AbsolutePrecision(f)-1;

   return &+[R|Coefficient(f,n*ell)*q^n : n in [1..prec div ell]] + 
        (1/ell) * (&+[R|Coefficient(f,n)*q^(n*ell) : n in [1..prec div (ell^2)]]); 
end intrinsic;
