 The ring formula_52 has Krull dimension one, and is the ring of regular functions of a projective algebraic set formula_53 of dimension 0 consisting of a finite number of points, which may be multiple points.As formula_54 belongs to a regular sequence, none of these points belong to the hyperplane of equation formula_55 The complement of this hyperplane is an affine space that contains formula_56 This makes formula_53 an affine algebraic set, which has formula_58 as its ring of regular functions.The linear polynomial formula_59 is not a zero divisor in formula_60 and one has thus an exact sequence
which implies that 
Here we are using Hilbert series of filtered algebras, and the fact that the Hilbert series of a graded algebra is also its Hilbert series as filtered algebra.