Journal of Inequalities in Pure and Applied Mathematics AN EXPLICIT MERTENS’ TYPE INEQUALITY FOR ARITHMETIC PROGRESSIONS volume 6, issue 3, article 67, 2005. OLIVIER BORDELLÈS 2 allée de la combe La Boriette 43000 Aiguilhe, France. Received 27 September, 2004; accepted 04 May, 2005. Communicated by: J. Sándor EMail: borde43@wanadoo.fr Abstract Contents JJ J II I Home Page Go Back Close c 2000 Victoria University ISSN (electronic): 1443-5756 172-04 Quit Abstract We give an explicit Mertens type formula for primes in arithmetic progressions using mean values of Dirichlet L-functions at s = 1. 2000 Mathematics Subject Classification: 11N13, 11M20 Key words: Mertens’ formula, Arithmetic progressions, Mean values of Dirichlet L−functions. Contents 1 2 3 4 Introduction and Main Result . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Sums with Primes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 The Polyá-Vinogradov Inequality and Character Sums with Primes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5 Mean Value Estimates of Dirichlet L−functions . . . . . . . . . . . 12 6 Proof of the Theorem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 References An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès Title Page Contents JJ J II I Go Back Close Quit Page 2 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au 1. Introduction and Main Result The very useful Mertens’ formula states that Y 1 1 e−γ = 1+O 1− p log x log x p≤x for any real number x ≥ 2, where γ ≈ 0.577215664 . . . denotes the Euler constant. Some explicit inequalities have been given in [4] where it is showed for example that −1 Y 1 (1.1) < eγ δ (x) log x, 1− p p≤x An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès where 1 δ (x) := 1 + . (log x)2 (1.2) Let 1 ≤ l ≤ k be positive integers satisfying (k, l) = 1. The aim of this paper is to provide an explicit upper bound for the product −1 Y 1 (1.3) 1− . p p≤x p≡l (mod k) In [2, 5], the authors gave asymptotic formulas for (1.3) in the form Y 1 1− ∼ c (k, l) (log x)−1/ϕ(k) , p p≤x p≡l (mod k) Title Page Contents JJ J II I Go Back Close Quit Page 3 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au where ϕ is the Euler totient function and c (k, l) is a constant depending on l and k. Nevertheless, because of the non-effectivity of the Siegel-Walfisz theorem, one cannot compute the implied constant in the error term. Moreover, the constant c (k, l) is given only for some particular cases in [2], whereas K.S. Williams established a quite complicated expression of c (k, l) involving a product of Dirichlet L−functions L (s; χ) and a function K (s; χ) at s = 1, where K (s; χ) is the generating Dirichlet series of the completely multiplicative function kχ defined by ( −χ(p) ) 1 χ (p) kχ (p) := p 1 − 1 − 1− p p An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès for any prime number p and any Dirichlet character χ modulo k. The author then gave explicit expressions of c (k, l) in the case k = 24. It could be useful to have an explicit upper bound for (1.3) valid for a large range of k and x. Indeed, we shall see in a forthcoming paper that such a bound could be used to estimate class numbers of certain cyclic number fields. We prove the following result: Theorem 1.1. Let 1 ≤ l ≤ k be positive integers satisfying (k, l) = 1 and k ≥ 37, and x be a positive real number such that x > k. We have: Y p≤x p≡l (mod k) 1− 1 p −1 Title Page Contents JJ J II I Go Back Close Quit Page 4 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au v 1 γ ϕ(k) u Y e ϕ (k) 1 2(γ−B) u tζ (2) <e 1− 2 · log x · Φ (x, k) , p k p|k where ( Φ (x, k) := exp 2 log x !) √ √ 2 k log k X L 0 (1; χ) + 2 k log k + E − γ , ϕ (k) χ6=χ L 0 B ≈ 0.261497212847643 . . . and E ≈ 1.332582275733221 . . . The restriction k ≥ 37 is given here just to use a simpler expression of the Polyá-Vinogradov inequality, but one can prove a similar result with k ≥ 9 only, the constants in Φ (x, k) being slightly larger. An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès Title Page Contents JJ J II I Go Back Close Quit Page 5 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au 2. Notation p denotes always a prime, 1 ≤ l ≤ k are positive integers satisfying (k, l) = 1 and k ≥ 37, x > k is a real number, ! n X 1 γ := lim − log n ≈ 0.5772156649015328 . . . n→∞ k k=1 is the Euler constant and γ1 := lim n→∞ n X log k k=1 k (log n)2 − 2 ! ≈ −0.07281584548367 . . . An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès is the first Stieltjes constant. Similarly, E := lim n→∞ log n − X log p p≤n ! B := lim n→∞ X1 p≤n p ≈ 1.332582275733221 . . . p and Title Page ! − log log n ≈ 0.261497212847643 . . . χ denotes a Dirichlet character modulo k and χ0 is the principal character modulo k. For anyP Dirichlet character χ modulo k and any s ∈ C such that ReP s > 1, ∞ χ(n) L (s; χ) := n=1 ns is the Dirichlet L− function associated to χ. χ6=χ0 means that the sum is taken over all non-principal characters modulo k. Λ is the Von Mangoldt function and f ∗ g denotes the usual Dirichlet convolution product. Contents JJ J II I Go Back Close Quit Page 6 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au 3. Sums with Primes From [4] we get the following estimates: Lemma 3.1. X p ∞ X 1 log p =E−γ pα α=2 and ∞ XX 1 = γ − B. αpα p α=2 An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès Title Page Contents JJ J II I Go Back Close Quit Page 7 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au 4. The Polyá-Vinogradov Inequality and Character Sums with Primes Lemma 4.1. Let χ be any non-principal Dirichlet character modulo k ≥ 37. (i) For any real number x ≥ 1, X 9√ k log k. χ (n) < 10 n≤x (ii) Let F ∈ C 1 ([1; +∞[ , [0; +∞[) such that F (t) & 0. For any real numt→∞ ber x ≥ 1, X 9 √ χ (n) F (n) ≤ F (x) k log k. n>x 5 (iii) For any real number x > k, 0 X χ (p) √ L 2 2 k log k (1; χ) + 1 + E − γ . < log x L p p>x An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès Title Page Contents JJ J II I Go Back Close Proof. (i) The result follows from Qiu’s improvement of the Polyá-Vinogradov inequality (see [3, p. 392]). (ii) Abel summation and (i). Quit Page 8 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au (iii) Let χ 6= χ0 be a Dirichlet character modulo k ≥ 37 and x > k be any real number. ( 1, if n = 1 (a) Since χ (µ ∗ 1) = ε where ε (n) = and 1 (n) = 1, 0, otherwise we get: X µ (d) χ (d) X χ (m) =1 d m d≤x m≤x/d and hence, since χ 6= χ0 , X µ (d) χ (d) d≤x d X X µ (d) χ (d) χ (m) 1 = + 1 L (1; χ) d≤x d m Olivier Bordellès m>x/d and thus, using (ii), √ √ X µ (d) χ (d) 9 k log k + 1 2 k log k (4.1) < . ≤ 5 d |L (1; χ)| |L (1; χ)| d≤x (b) Since log = Λ ∗ 1, we get: X χ (n) Λ (n) n≤x An Explicit Mertens’ Type Inequality for Arithmetic Progressions n Title Page Contents JJ J II I Go Back X µ (d) χ (d) X χ (m) log m d m d≤x m≤x/d X X X χ (m) log m = + m = d≤x/e x/e<d≤x m≤x/d Close Quit Page 9 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au = X µ (d) χ (d) X χ (m) log m χ (2) log 2 + d m 2 d≤x/e = −L 0 (1; χ) m≤x/d x/e<d≤x µ (d) χ (d) d X µ (d) χ (d) X µ (d) χ (d) X χ (m) log m − d d m d≤x/e + X χ (2) log 2 2 d≤x/e X x/e<d≤x m>x/d µ (d) χ (d) d and, by using (ii), (4.1) and the trivial bound for the third sum, we get: X χ (n) Λ (n) (4.2) n n≤x 0 √ L < k log k 2 (1; χ) L X 9 x log 2 e + log + 1+ 5x d 2 x d≤x/e 0 √ 18 log 2 L e + 1+ ≤ k log k 2 (1; χ) + L 5e 2 37 0 √ L < 2 k log k (1; χ) + 1 L since x > q ≥ 37. An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès Title Page Contents JJ J II I Go Back Close Quit Page 10 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au (c) By Abel summation, we get: X χ (p) log p X χ (p) 2 max ≤ . log x t≥x p p p>x p≤t Moreover, X χ (p) log p p≤t p = X χ (n) Λ (n) n≤t n − ∞ XX χ (pα ) log p p α=2 pα ≤t pα and then: ∞ X χ (p) log p X χ (n) Λ (n) X X 1 ≤ + log p p n pα p α=2 p≤t n≤t X χ (n) Λ (n) = +E−γ n n≤t 0 √ L < 2 k log k (1; χ) + 1 + E − γ L by (4.2) . This concludes the proof of Lemma 4.1. An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès Title Page Contents JJ J II I Go Back Close Quit Page 11 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au Mean Value Estimates of Dirichlet L−functions 5. Lemma 5.1. (i) For any positive integers j, k, jk X X log p c0 (j, k) 2ω(k) 1 ϕ (k) = log (jk) + γ + + n k p − 1 jk n=1 p|k (n,k)=1 where ω (k) := P p|k An Explicit Mertens’ Type Inequality for Arithmetic Progressions 1 and |c0 (j, k)| ≤ 1. (ii) For any positive integer k ≥ 9, Olivier Bordellès k ϕ (k) 2 ζ (2) Y p|k 1− 2 X log p 1 π2 ≤ 0. +2γ +γ+ − log k + 1 p2 3 p−1 Title Page p|k Contents (iii) For any positive integer k ≥ 9, Y |L (1; χ)|1/ϕ(k) χ6=χ0 1 Y p 1 2 ≤ ζ (2) 1− 2 . p p|k JJ J II I Go Back Proof. Close (i) Quit jk X 1 X µ (d) X 1 X µ (d) jk ε (d) d = = log +γ+ n d n d d jk n=1 (n,k)=1 d|k n≤jk/d d|k Page 12 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au where |ε (d)| ≤ 1 and hence: jk X X µ (d) X µ (d) log d 1 X 1 = {log (jk) + γ} − + ε (d) µ (d) n d d jk n=1 d|k (n,k)=1 d|k d|k and we conclude by noting that X µ (d) d d|k X µ (d) log d d d|k = =− ϕ (k) , k An Explicit Mertens’ Type Inequality for Arithmetic Progressions ϕ (k) X log p k p−1 Olivier Bordellès p|k Title Page and X X ε (d) µ (d) ≤ µ2 (d) = 2ω(k) . d|k d|k Contents JJ J (ii) Define A (k) := k ϕ (k) II I Go Back 2 ζ (2) Y p|k 1 1− 2 p Close 2 + 2γ1 + γ + X log p π2 . − log k + 3 p−1 p|k Quit Page 13 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au Using [1] we check the inequality for 9 ≤ k ≤ 513 and then suppose k ≥ 514. Since Y p Y 1 k p p−1 = ≤ ϕ (k) p−1 p|k p|k we have taking logarithms X log p k k ≥ log ≥ log p−1 ϕ (k) k−1 p|k An Explicit Mertens’ Type Inequality for Arithmetic Progressions and from the inequality ([4]) 2.50637 k < eγ log log k + ϕ (k) log log k Olivier Bordellès Title Page valid for any integer k ≥ 3, we obtain Contents 2 2.50637 log log k 2 2 π2 k + 2γ1 + γ + − log <0 3 k−1 A (k) ≤ ζ (2) eγ log log k + JJ J II I Go Back Close if k ≥ 514. Quit (iii) First, X χ6=χ0 |L (1; χ)|2 = lim S (N ) Page 14 of 24 N →∞ J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au where S (N ) := Nk X χ (n) χ (m) − nm m,n=1 Nk X n=1 (n,k)=1 2 1 . n Following a standard argument, we have using (i): S (N ) = ϕ (k) Nk X m6=n=1 m≡n (mod k) (n,k)=(m,k)=1 = ϕ (k) 1 − mn Nk X 1 + ϕ (k) n2 n=1 (n,k)=1 ≤ ϕ (k) ζ (2) Y p|k + 2ϕ (k) 1 1− 2 p −j)k N (N X X j=1 n=1 (n,k)=1 Nk X n=1 (n,k)=1 2 An Explicit Mertens’ Type Inequality for Arithmetic Progressions 1 n Nk X m6=n=1 m≡n (mod k) (n,k)=(m,k)=1 Olivier Bordellès 2 Nk 1 X 1 − mn n n=1 Title Page Contents (n,k)=1 JJ J 1 − n (n + jk) Nk X n=1 (n,k)=1 2 1 n II I Go Back Close Quit Page 15 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au 1 = ϕ (k) ζ (2) 1− 2 p p|k 2 (N −j)k N k N N k X 1 X 1 2ϕ (k) X 1 X 1 + − − k j=1 j n n=1+jk n n n=1 n=1 Y (n,k)=1 ≤ ϕ (k) ζ (2) Y 1− p|k = ϕ (k) ζ (2) Y 1− p|k 1 p2 1 p2 + (n,k)=1 (n,k)=1 2ϕ (k) k N X j=1 jk 1 X 1 − j n=1 n (n,k)=1 Nk X n=1 (n,k)=1 2 1 n Olivier Bordellès ω(k) X log p c0 (j, k) 2 ϕ (k) log (jk) + γ + + + k j=1 j k p − 1 jk p|k 2 ω(k) X ϕ (k) log p c0 (N, k) 2 . − log (N k) + γ + + k p − 1 Nk N 2ϕ (k) X 1 An Explicit Mertens’ Type Inequality for Arithmetic Progressions p|k We now neglect the dependance of c0 in k. Since M X 1 c1 (M ) = log M + γ + m M m=1 Title Page Contents JJ J II I Go Back Close Quit Page 16 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au and M X (log M )2 c2 (M ) log M log m = + γ1 + , m 2 M m=1 where 0 < c1 (M ) ≤ 1 2 and |c2 (M )| ≤ 1, we get: Y 1 S (N ) ≤ ϕ (k) ζ (2) 1− 2 p p|k 2 ϕ (k) 2c2 (N ) log N + (log N )2 + 2γ1 + k N X log p c (N ) 1 log N + γ + + 2 log k + γ + p−1 N p|k 2 X log p − log (N k) + γ + p−1 p|k ( N 2ω(k)+1 ϕ (k) X c0 (j) + k2 j2 j=1 X c0 (N ) log p 22ω(k) c20 (N ) log (N k) + γ + − − N p−1 N 2k2 An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès Title Page Contents JJ J II I Go Back Close Quit p|k Page 17 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au 1 = ϕ (k) ζ (2) 1− 2 p p|k 2 2 X ϕ (k) log p + 2γ1 + γ − log k + k p−1 p|k X 2c1 (N ) log p 2c2 (N ) log N + log k + γ + + N p−1 N p|k ( N 2ω(k)+1 ϕ (k) X c0 (j) + k2 j2 j=1 X log p 22ω(k) c20 (N ) c0 (N ) log (N k) + γ + − − N p−1 N 2k2 Y p|k lim S (N ) ≤ ϕ (k) ζ (2) N →∞ p|k + 1 1− 2 p Olivier Bordellès Title Page Contents JJ J and then Y An Explicit Mertens’ Type Inequality for Arithmetic Progressions II I Go Back Close 2 2 X ϕ (k) log p 2γ1 + γ − log k + k p−1 Quit p|k ω(k) + 2 ϕ (k) π 3k 2 Page 18 of 24 2 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au and the inequality 2ω(k) ≤ ϕ (k) (valid for any integer k ≥ 3 and 6= 6) implies Y 1 lim S (N ) ≤ ϕ (k) ζ (2) 1− 2 N →∞ p p|k 2 2 2 X π log p ϕ (k) + 2γ1 + γ + − log k + k 3 p−1 p|k Y 1 = (ϕ (k) − 1) ζ (2) 1− 2 p p|k 2 2 Y ϕ (k) k 1 + ζ (2) 1− 2 ϕ (k) k p p|k 2 2 X π log p +2γ1 + γ + − log k + 3 p−1 p|k Y 1 ≤ (ϕ (k) − 1) ζ (2) 1− 2 p p|k An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès Title Page Contents JJ J II I Go Back Close if k ≥ 9 by (ii). Hence Quit X Y 1 1 2 |L (1; χ)| ≤ ζ (2) 1− 2 . ϕ (k) − 1 χ6=χ p 0 p|k Page 19 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au Now the IAG inequality implies: ( ) Y X 1 1 |L (1; χ)| ϕ(k) = exp log |L (1; χ)|2 2ϕ (k) χ6=χ0 χ6=χ0 ( !) X ϕ (k) − 1 1 ≤ exp log |L (1; χ)|2 2ϕ (k) ϕ (k) − 1 χ6=χ 0 ≤ ζ (2) Y p|k ≤ ζ (2) Y p|k ϕ(k)−1 2ϕ(k) 1 1− 2 p 1− 12 1 . p2 An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès Title Page Contents JJ J II I Go Back Close Quit Page 20 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au 6. Proof of the Theorem Lemma 6.1. If χ0 is the principal character modulo k and if x > k, then: Y p≤x 1 1− p −χ0 (p) < eγ ϕ (k) δ (x) · log x, k where δ is the function defined in (1.2). An Explicit Mertens’ Type Inequality for Arithmetic Progressions Proof. Since x > k, Y p≤x p|k 1 1− p = Y p|k 1 1− p = ϕ (k) k Olivier Bordellès Title Page and then Y p≤x 1− 1 p −χ0 (p) = Y p≤x p-k = Y p≤x = and we use (1.1) . 1− 1 p 1 1− p Contents −1 JJ J −1 Y Y p≤x p|k ϕ (k) 1 1− k p≤x p 1 1− p −1 II I Go Back Close Quit Page 21 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au Proof of the theorem. Let 1 ≤ l ≤ k be positive integers satisfying (k, l) = 1 and k ≥ 37, and x be a positive real number such that x > k. We have: −ϕ(k) Y −χ0 (p) Y Y −χ(p) !χ(l) Y 1 1 1 1− = 1− · 1− p p p p≤x p≤x p≤x χ6=χ 0 p≡l (mod k) := Π1 × Π2 eγ ϕ (k) δ (x) with Π1 < · log x by Lemma 6.1. Moreover, k ( !) X X 1 Π2 = exp χ (l) − χ (p) log 1 − p p≤x χ6=χ0 ! ∞ X XX χ (p) = exp χ (l) αpα p≤x α=1 χ6=χ0 !) ( ∞ X X χ (p) X X χ (p) + = exp χ (l) p αpα p≤x p≤x α=2 χ6=χ An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès Title Page Contents JJ J 0 Go Back and if χ 6= χ0 , we have L (1; χ) = Y p = exp II I χ (p) 1− p X χ (p) p≤x p Close −1 Quit + X χ (p) p>x p + ∞ XX χ (pα ) p α=2 αpα ! Page 22 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au and thus Π2 = Y L (1; χ)χ(l) χ6=χ0 ( × exp X χ (l) − X χ (p) p>x χ6=χ0 p + ∞ XX χ (p) p≤x α=2 αpα − ∞ XX χ (pα ) p α=2 !) αpα and hence ) ∞ XX Y X X χ (p) 1 |Π2 | ≤ |L (1; χ)| · exp + 2 (ϕ (k) − 1) p αpα p α=2 χ6=χ0 χ6=χ0 p>x !) ( Y X X χ (p) = e2(ϕ(k)−1)(γ−B) |L (1; χ)| · exp p p>x ( χ6=χ0 An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès Title Page χ6=χ0 Contents and we use Lemma 4.1 (iii) and Lemma 5.1 (iii). We conclude the proof by δ(x) < 1. noting that, if x > 37, e2(γ−B) JJ J II I Go Back Close Quit Page 23 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au References [1] PARI/GP, Available by anonymous ftp from the URL: ftp://megrez. math.u-bordeaux.fr/pub/pari. [2] E. GROSSWALD, Some number theoretical products, Rev. Colomb. Mat., 21 (1987), 231–242. [3] D.S. MITRINOVIĆ AND J. SÁNDOR (in cooperation with B. CRSTICI), Handbook of Number Theory, Kluwer Acad. Publishers, ISBN: 0-79233823-5. [4] J.B. ROSSER AND L. SCHŒNFELD, Approximate formulas for some functions of prime numbers, Illinois J. Math., 6 (1962), 64–94. [5] K.S. WILLIAMS, Mertens’ theorem for arithmetic progressions, J. Number Theory, 6 (1974), 353–359. An Explicit Mertens’ Type Inequality for Arithmetic Progressions Olivier Bordellès Title Page Contents JJ J II I Go Back Close Quit Page 24 of 24 J. Ineq. Pure and Appl. Math. 6(3) Art. 67, 2005 http://jipam.vu.edu.au