 More precisely, "D""X" is equipped with the "Bernstein filtration", that is, the filtration such that "F""p""A""n"("K") consists of "K"-linear combinations of differential operators "x""α"∂"β" with |"α"| + |"β"| ≤ "p" (using multiindex notation).The associated graded ring is seen to be isomorphic to the polynomial ring in 2"n" indeterminates.In particular it is commutative.