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<art>
   <ui>1029-242X-2011-592840</ui>
   <ji>1029-242X</ji>
   <fm>
      <dochead>Research Article</dochead>
      <bibl>
         <title>
            <p>Some New Double Sequence Spaces Defined by Orlicz Function in <inline-formula><graphic file="1029-242X-2011-592840-i1.gif"/></inline-formula>-Normed Space</p>
         </title>
         <aug>
            <au ca="yes" id="A1"><snm>Sava&#351;</snm><fnm>Ekrem</fnm><insr iid="I1"/><email>ekremsavas@yahoo.com</email></au>
         </aug>
         <insg>
            <ins id="I1"><p>Department of Mathematics, Istanbul Commerce University, Uskudar, 34672 Istanbul, Turkey</p></ins>
         </insg>
         <source>Journal of Inequalities and Applications</source>
         <issn>1029-242X</issn>
         <pubdate>2011</pubdate>
         <volume>2011</volume>
         <issue>1</issue>
         <fpage>592840</fpage>
         <url>http://www.journalofinequalitiesandapplications.com/content/2011/1/592840</url>
         <xrefbib><pubid idtype="doi">10.1155/2011/592840</pubid></xrefbib>
      </bibl>
      <history><rec><date><day>1</day><month>1</month><year>2011</year></date></rec><acc><date><day>17</day><month>2</month><year>2011</year></date></acc><pub><date><day>9</day><month>3</month><year>2011</year></date></pub></history>
      <cpyrt><year>2011</year><collab>Ekrem Sava&#351;.</collab><note>This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.</note></cpyrt>
      <abs>
         <sec>
            <st>
               <p/>
            </st>
            <p>The aim of this paper is to introduce and study some new double sequence spaces with respect to an Orlicz function, and also some properties of the resulting sequence spaces were examined.</p>
         </sec>
      </abs>
   </fm>
   <bdy>
      <sec>
         <st>
            <p>1. Introduction</p>
         </st>
         <p>We recall that the concept of a 2-normed space was first given in the works of G&#228;hler ([<abbr bid="B1">1</abbr>, <abbr bid="B2">2</abbr>]) as an interesting nonlinear generalization of a normed linear space which was subsequently studied by many authors (see, [<abbr bid="B3">3</abbr>, <abbr bid="B4">4</abbr>]). Recently, a lot of activities have started to study summability, sequence spaces, and related topics in these nonlinear spaces (see, e.g., [<abbr bid="B5">5</abbr>&#8211;<abbr bid="B9">9</abbr>]). In particular, Sava&#351; [<abbr bid="B10">10</abbr>] combined Orlicz function and ideal convergence to define some sequence spaces using 2-norm.</p>
         <p>In this paper, we introduce and study some new double-sequence spaces, whose elements are form <inline-formula><graphic file="1029-242X-2011-592840-i2.gif"/></inline-formula>-normed spaces, using an Orlicz function, which may be considered as an extension of various sequence spaces to <inline-formula><graphic file="1029-242X-2011-592840-i3.gif"/></inline-formula>-normed spaces. We begin with recalling some notations and backgrounds.</p>
         <p>Recall in [<abbr bid="B11">11</abbr>] that an Orlicz function <inline-formula><graphic file="1029-242X-2011-592840-i4.gif"/></inline-formula> is continuous, convex, and nondecreasing function such that <inline-formula><graphic file="1029-242X-2011-592840-i5.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i6.gif"/></inline-formula> for <inline-formula><graphic file="1029-242X-2011-592840-i7.gif"/></inline-formula>, and <inline-formula><graphic file="1029-242X-2011-592840-i8.gif"/></inline-formula> as <inline-formula><graphic file="1029-242X-2011-592840-i9.gif"/></inline-formula>.</p>
         <p>Subsequently, Orlicz function was used to define sequence spaces by Parashar and Choudhary [<abbr bid="B12">12</abbr>] and others. An Orlicz function <inline-formula><graphic file="1029-242X-2011-592840-i10.gif"/></inline-formula> can always be represented in the following integral form: <inline-formula><graphic file="1029-242X-2011-592840-i11.gif"/></inline-formula>, where <inline-formula><graphic file="1029-242X-2011-592840-i12.gif"/></inline-formula> is the known kernel of <inline-formula><graphic file="1029-242X-2011-592840-i13.gif"/></inline-formula>, right differential for <inline-formula><graphic file="1029-242X-2011-592840-i14.gif"/></inline-formula>, <inline-formula><graphic file="1029-242X-2011-592840-i15.gif"/></inline-formula>, <inline-formula><graphic file="1029-242X-2011-592840-i16.gif"/></inline-formula> for <inline-formula><graphic file="1029-242X-2011-592840-i17.gif"/></inline-formula>, <inline-formula><graphic file="1029-242X-2011-592840-i18.gif"/></inline-formula> is nondecreasing, and <inline-formula><graphic file="1029-242X-2011-592840-i19.gif"/></inline-formula> as <inline-formula><graphic file="1029-242X-2011-592840-i20.gif"/></inline-formula>.</p>
         <p>If convexity of Orlicz function <inline-formula><graphic file="1029-242X-2011-592840-i21.gif"/></inline-formula> is replaced by <inline-formula><graphic file="1029-242X-2011-592840-i22.gif"/></inline-formula>, then this function is called Modulus function, which was presented and discussed by Ruckle [<abbr bid="B13">13</abbr>] and Maddox [<abbr bid="B14">14</abbr>].</p>
         <p>Remark 1.1. </p>
         <p>If <inline-formula><graphic file="1029-242X-2011-592840-i23.gif"/></inline-formula> is a convex function and <inline-formula><graphic file="1029-242X-2011-592840-i24.gif"/></inline-formula>, then <inline-formula><graphic file="1029-242X-2011-592840-i25.gif"/></inline-formula> for all <inline-formula><graphic file="1029-242X-2011-592840-i26.gif"/></inline-formula> with <inline-formula><graphic file="1029-242X-2011-592840-i27.gif"/></inline-formula>.</p>
         <p>Let <inline-formula><graphic file="1029-242X-2011-592840-i28.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i29.gif"/></inline-formula> be real vector space of dimension <inline-formula><graphic file="1029-242X-2011-592840-i30.gif"/></inline-formula>, where <inline-formula><graphic file="1029-242X-2011-592840-i31.gif"/></inline-formula>. An <inline-formula><graphic file="1029-242X-2011-592840-i32.gif"/></inline-formula>-norm on <inline-formula><graphic file="1029-242X-2011-592840-i33.gif"/></inline-formula> is a function <inline-formula><graphic file="1029-242X-2011-592840-i34.gif"/></inline-formula> which satisfies the following four conditions:</p>
         <p indent="1">(i)<inline-formula><graphic file="1029-242X-2011-592840-i35.gif"/></inline-formula> if and only if <inline-formula><graphic file="1029-242X-2011-592840-i36.gif"/></inline-formula> are linearly dependent,</p>
         <p indent="1">(ii)<inline-formula><graphic file="1029-242X-2011-592840-i37.gif"/></inline-formula> are invariant under permutation,</p>
         <p indent="1">(iii)<inline-formula><graphic file="1029-242X-2011-592840-i38.gif"/></inline-formula>, <inline-formula><graphic file="1029-242X-2011-592840-i39.gif"/></inline-formula>,</p>
         <p indent="1">(iv)<inline-formula><graphic file="1029-242X-2011-592840-i40.gif"/></inline-formula>. </p>
         <p/>
         <p>The pair <inline-formula><graphic file="1029-242X-2011-592840-i41.gif"/></inline-formula> is then called an <inline-formula><graphic file="1029-242X-2011-592840-i42.gif"/></inline-formula>-normed space [<abbr bid="B3">3</abbr>].</p>
         <p>Let <inline-formula><graphic file="1029-242X-2011-592840-i43.gif"/></inline-formula> be equipped with the <inline-formula><graphic file="1029-242X-2011-592840-i44.gif"/></inline-formula>-norm, then <inline-formula><graphic file="1029-242X-2011-592840-i45.gif"/></inline-formula> the volume of the <inline-formula><graphic file="1029-242X-2011-592840-i46.gif"/></inline-formula>-dimensional parallelepiped spanned by the vectors, <inline-formula><graphic file="1029-242X-2011-592840-i47.gif"/></inline-formula> which may be given explicitly by the formula</p>
         <p>
            <display-formula id="M11">
               <graphic file="1029-242X-2011-592840-i48.gif"/>
            </display-formula>
         </p>
         <p>where <inline-formula><graphic file="1029-242X-2011-592840-i49.gif"/></inline-formula> denotes inner product. Let <inline-formula><graphic file="1029-242X-2011-592840-i50.gif"/></inline-formula> be an <inline-formula><graphic file="1029-242X-2011-592840-i51.gif"/></inline-formula>-normed space of dimension <inline-formula><graphic file="1029-242X-2011-592840-i52.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i53.gif"/></inline-formula> a linearly independent set in <inline-formula><graphic file="1029-242X-2011-592840-i54.gif"/></inline-formula>. Then, the function <inline-formula><graphic file="1029-242X-2011-592840-i55.gif"/></inline-formula> on <inline-formula><graphic file="1029-242X-2011-592840-i56.gif"/></inline-formula> is defined by </p>
         <p>
            <display-formula id="M12">
               <graphic file="1029-242X-2011-592840-i57.gif"/>
            </display-formula>
         </p>
         <p>is defines an <inline-formula><graphic file="1029-242X-2011-592840-i58.gif"/></inline-formula> norm on <inline-formula><graphic file="1029-242X-2011-592840-i59.gif"/></inline-formula> with respect to <inline-formula><graphic file="1029-242X-2011-592840-i60.gif"/></inline-formula> (see, [<abbr bid="B15">15</abbr>]).</p>
         <p>Definition 1.2 (see [<abbr bid="B7">7</abbr>]). </p>
         <p>A sequence <inline-formula><graphic file="1029-242X-2011-592840-i61.gif"/></inline-formula> in <inline-formula><graphic file="1029-242X-2011-592840-i62.gif"/></inline-formula>-normed space <inline-formula><graphic file="1029-242X-2011-592840-i63.gif"/></inline-formula> is aid to be convergent to an <inline-formula><graphic file="1029-242X-2011-592840-i64.gif"/></inline-formula> in <inline-formula><graphic file="1029-242X-2011-592840-i65.gif"/></inline-formula> (in the <inline-formula><graphic file="1029-242X-2011-592840-i66.gif"/></inline-formula>-norm) if </p>
         <p>
            <display-formula id="M13">
               <graphic file="1029-242X-2011-592840-i67.gif"/>
            </display-formula>
         </p>
         <p>for every <inline-formula><graphic file="1029-242X-2011-592840-i68.gif"/></inline-formula>.</p>
         <p>Definition 1.3 (see [<abbr bid="B16">16</abbr>]). </p>
         <p>Let <inline-formula><graphic file="1029-242X-2011-592840-i69.gif"/></inline-formula> be a linear space. Then, a map <inline-formula><graphic file="1029-242X-2011-592840-i70.gif"/></inline-formula> is called a paranorm (on <inline-formula><graphic file="1029-242X-2011-592840-i71.gif"/></inline-formula>) if it is satisfies the following conditions for all <inline-formula><graphic file="1029-242X-2011-592840-i72.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i73.gif"/></inline-formula> scalar:</p>
         <p indent="1">(i)<inline-formula><graphic file="1029-242X-2011-592840-i74.gif"/></inline-formula>&#8201;&#8201;<inline-formula><graphic file="1029-242X-2011-592840-i75.gif"/></inline-formula>,</p>
         <p indent="1">(ii)<inline-formula><graphic file="1029-242X-2011-592840-i76.gif"/></inline-formula>, </p>
         <p indent="1">(iii)<inline-formula><graphic file="1029-242X-2011-592840-i77.gif"/></inline-formula>, </p>
         <p indent="1">(iv)<inline-formula><graphic file="1029-242X-2011-592840-i78.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i79.gif"/></inline-formula> imply <inline-formula><graphic file="1029-242X-2011-592840-i80.gif"/></inline-formula>.</p>
         <p/>
      </sec>
      <sec>
         <st>
            <p>2. Main Results</p>
         </st>
         <p>Let <inline-formula><graphic file="1029-242X-2011-592840-i81.gif"/></inline-formula> be any <inline-formula><graphic file="1029-242X-2011-592840-i82.gif"/></inline-formula>-normed space, and let <inline-formula><graphic file="1029-242X-2011-592840-i83.gif"/></inline-formula> denote <inline-formula><graphic file="1029-242X-2011-592840-i84.gif"/></inline-formula>-valued sequence spaces. Clearly <inline-formula><graphic file="1029-242X-2011-592840-i85.gif"/></inline-formula> is a linear space under addition and scalar multiplication.</p>
         <p>Definition 2.1. </p>
         <p>Let <inline-formula><graphic file="1029-242X-2011-592840-i86.gif"/></inline-formula> be an Orlicz function and <inline-formula><graphic file="1029-242X-2011-592840-i87.gif"/></inline-formula> any <inline-formula><graphic file="1029-242X-2011-592840-i88.gif"/></inline-formula>-normed space. Further, let <inline-formula><graphic file="1029-242X-2011-592840-i89.gif"/></inline-formula> be a bounded sequence of positive real numbers. Now, we define the following new double sequence space as follows: </p>
         <p>
            <display-formula id="M21">
               <graphic file="1029-242X-2011-592840-i90.gif"/>
            </display-formula>
         </p>
         <p>for each <inline-formula><graphic file="1029-242X-2011-592840-i91.gif"/></inline-formula>.</p>
         <p>The following inequalities will be used throughout the paper. Let <inline-formula><graphic file="1029-242X-2011-592840-i92.gif"/></inline-formula> be a double sequence of positive real numbers with <inline-formula><graphic file="1029-242X-2011-592840-i93.gif"/></inline-formula>, and let <inline-formula><graphic file="1029-242X-2011-592840-i94.gif"/></inline-formula>. Then, for the factorable sequences <inline-formula><graphic file="1029-242X-2011-592840-i95.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i96.gif"/></inline-formula> in the complex plane, we have as in Maddox [<abbr bid="B16">16</abbr>] </p>
         <p>
            <display-formula id="M22">
               <graphic file="1029-242X-2011-592840-i97.gif"/>
            </display-formula>
         </p>
         <p/>
         <p>Theorem 2.2. </p>
         <p><inline-formula><graphic file="1029-242X-2011-592840-i98.gif"/></inline-formula> sequences space is a linear space.</p>
         <p>Proof. </p>
         <p>Now, assume that <inline-formula><graphic file="1029-242X-2011-592840-i99.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i100.gif"/></inline-formula>. Then, </p>
         <p>
            <display-formula id="M23">
               <graphic file="1029-242X-2011-592840-i101.gif"/>
            </display-formula>
         </p>
         <p>Since <inline-formula><graphic file="1029-242X-2011-592840-i102.gif"/></inline-formula> is a <inline-formula><graphic file="1029-242X-2011-592840-i103.gif"/></inline-formula>-norm on <inline-formula><graphic file="1029-242X-2011-592840-i104.gif"/></inline-formula>, and <inline-formula><graphic file="1029-242X-2011-592840-i105.gif"/></inline-formula> is an Orlicz function, we get </p>
         <p>
            <display-formula id="M24">
               <graphic file="1029-242X-2011-592840-i106.gif"/>
            </display-formula>
         </p>
         <p>where </p>
         <p>
            <display-formula id="M25">
               <graphic file="1029-242X-2011-592840-i107.gif"/>
            </display-formula>
         </p>
         <p>and this completes the proof.</p>
         <p>Theorem 2.3. </p>
         <p><inline-formula><graphic file="1029-242X-2011-592840-i108.gif"/></inline-formula> space is a paranormed space with the paranorm defined by <inline-formula><graphic file="1029-242X-2011-592840-i109.gif"/></inline-formula></p>
         <p>
            <display-formula id="M26">
               <graphic file="1029-242X-2011-592840-i110.gif"/>
            </display-formula>
         </p>
         <p>where <inline-formula><graphic file="1029-242X-2011-592840-i111.gif"/></inline-formula>, <inline-formula><graphic file="1029-242X-2011-592840-i112.gif"/></inline-formula>.</p>
         <p>Proof. </p>
         <p>(i) Clearly, <inline-formula><graphic file="1029-242X-2011-592840-i113.gif"/></inline-formula> and (ii) <inline-formula><graphic file="1029-242X-2011-592840-i114.gif"/></inline-formula>. (iii) Let <inline-formula><graphic file="1029-242X-2011-592840-i115.gif"/></inline-formula>, then there exists <inline-formula><graphic file="1029-242X-2011-592840-i116.gif"/></inline-formula> such that </p>
         <p>
            <display-formula id="M27">
               <graphic file="1029-242X-2011-592840-i117.gif"/>
            </display-formula>
         </p>
         <p>So, we have </p>
         <p>
            <display-formula id="M28">
               <graphic file="1029-242X-2011-592840-i118.gif"/>
            </display-formula>
         </p>
         <p>and thus </p>
         <p>
            <display-formula id="M29">
               <graphic file="1029-242X-2011-592840-i119.gif"/>
            </display-formula>
         </p>
         <p>(iv) Now, let <inline-formula><graphic file="1029-242X-2011-592840-i120.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i121.gif"/></inline-formula>. Since </p>
         <p>
            <display-formula id="M210">
               <graphic file="1029-242X-2011-592840-i122.gif"/>
            </display-formula>
         </p>
         <p>This gives us <inline-formula><graphic file="1029-242X-2011-592840-i123.gif"/></inline-formula>.</p>
         <p>Theorem 2.4. </p>
         <p>If <inline-formula><graphic file="1029-242X-2011-592840-i124.gif"/></inline-formula> for each <inline-formula><graphic file="1029-242X-2011-592840-i125.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i126.gif"/></inline-formula>, then <inline-formula><graphic file="1029-242X-2011-592840-i127.gif"/></inline-formula>.</p>
         <p>Proof. </p>
         <p>If <inline-formula><graphic file="1029-242X-2011-592840-i128.gif"/></inline-formula>, then there exists some <inline-formula><graphic file="1029-242X-2011-592840-i129.gif"/></inline-formula> such that </p>
         <p>
            <display-formula id="M211">
               <graphic file="1029-242X-2011-592840-i130.gif"/>
            </display-formula>
         </p>
         <p>This implies that </p>
         <p>
            <display-formula id="M212">
               <graphic file="1029-242X-2011-592840-i131.gif"/>
            </display-formula>
         </p>
         <p>for sufficiently large values of <inline-formula><graphic file="1029-242X-2011-592840-i132.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i133.gif"/></inline-formula>. Since <inline-formula><graphic file="1029-242X-2011-592840-i134.gif"/></inline-formula> is nondecreasing, we are granted </p>
         <p>
            <display-formula id="M213">
               <graphic file="1029-242X-2011-592840-i135.gif"/>
            </display-formula>
         </p>
         <p>Thus, <inline-formula><graphic file="1029-242X-2011-592840-i136.gif"/></inline-formula>. This completes the proof.</p>
         <p>The following result is a consequence of the above theorem.</p>
         <p>Corollary 2.5. </p>
         <p>(i) If <inline-formula><graphic file="1029-242X-2011-592840-i137.gif"/></inline-formula> for each <inline-formula><graphic file="1029-242X-2011-592840-i138.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i139.gif"/></inline-formula>, then </p>
         <p>
            <display-formula id="M214">
               <graphic file="1029-242X-2011-592840-i140.gif"/>
            </display-formula>
         </p>
         <p/>
         <p>(ii) If <inline-formula><graphic file="1029-242X-2011-592840-i141.gif"/></inline-formula> for each <inline-formula><graphic file="1029-242X-2011-592840-i142.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i143.gif"/></inline-formula>, then </p>
         <p>
            <display-formula id="M215">
               <graphic file="1029-242X-2011-592840-i144.gif"/>
            </display-formula>
         </p>
         <p/>
         <p>Theorem 2.6. </p>
         <p><inline-formula><graphic file="1029-242X-2011-592840-i145.gif"/></inline-formula>, where <inline-formula><graphic file="1029-242X-2011-592840-i146.gif"/></inline-formula> is the double space of bounded sequences and <inline-formula><graphic file="1029-242X-2011-592840-i147.gif"/></inline-formula>.</p>
         <p>Proof. </p>
         <p><inline-formula><graphic file="1029-242X-2011-592840-i148.gif"/></inline-formula>. Then, there exists an <inline-formula><graphic file="1029-242X-2011-592840-i149.gif"/></inline-formula> such that <inline-formula><graphic file="1029-242X-2011-592840-i150.gif"/></inline-formula> for each <inline-formula><graphic file="1029-242X-2011-592840-i151.gif"/></inline-formula>, <inline-formula><graphic file="1029-242X-2011-592840-i152.gif"/></inline-formula>. We want to show <inline-formula><graphic file="1029-242X-2011-592840-i153.gif"/></inline-formula><inline-formula><graphic file="1029-242X-2011-592840-i154.gif"/></inline-formula>. But </p>
         <p>
            <display-formula id="M216">
               <graphic file="1029-242X-2011-592840-i155.gif"/>
            </display-formula>
         </p>
         <p>and this completes the proof.</p>
         <p>Theorem 2.7. </p>
         <p>Let <inline-formula><graphic file="1029-242X-2011-592840-i156.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i157.gif"/></inline-formula> be Orlicz function. Then, we have </p>
         <p>
            <display-formula id="M217">
               <graphic file="1029-242X-2011-592840-i158.gif"/>
            </display-formula>
         </p>
         <p/>
         <p>Proof. </p>
         <p>We have </p>
         <p>
            <display-formula id="M218">
               <graphic file="1029-242X-2011-592840-i159.gif"/>
            </display-formula>
         </p>
         <p>Let <inline-formula><graphic file="1029-242X-2011-592840-i160.gif"/></inline-formula>; when adding the above inequality from <inline-formula><graphic file="1029-242X-2011-592840-i161.gif"/></inline-formula> to <inline-formula><graphic file="1029-242X-2011-592840-i162.gif"/></inline-formula> we get <inline-formula><graphic file="1029-242X-2011-592840-i163.gif"/></inline-formula> and this completes the proof.</p>
         <p>Definition 2.8 (see [<abbr bid="B10">10</abbr>]). </p>
         <p>Let <inline-formula><graphic file="1029-242X-2011-592840-i164.gif"/></inline-formula> be a sequence space. Then, <inline-formula><graphic file="1029-242X-2011-592840-i165.gif"/></inline-formula> is called solid if <inline-formula><graphic file="1029-242X-2011-592840-i166.gif"/></inline-formula> whenever <inline-formula><graphic file="1029-242X-2011-592840-i167.gif"/></inline-formula> for all sequences <inline-formula><graphic file="1029-242X-2011-592840-i168.gif"/></inline-formula> of scalars with <inline-formula><graphic file="1029-242X-2011-592840-i169.gif"/></inline-formula> for all <inline-formula><graphic file="1029-242X-2011-592840-i170.gif"/></inline-formula>.</p>
         <p>Definition 2.9. </p>
         <p>Let <inline-formula><graphic file="1029-242X-2011-592840-i171.gif"/></inline-formula> be a sequence space. Then, <inline-formula><graphic file="1029-242X-2011-592840-i172.gif"/></inline-formula> is called monotone if it contains the canonical preimages of all its step spaces (see, [<abbr bid="B17">17</abbr>]).</p>
         <p>Theorem 2.10. </p>
         <p>The sequence space <inline-formula><graphic file="1029-242X-2011-592840-i173.gif"/></inline-formula> is solid.</p>
         <p>Proof. </p>
         <p>Let <inline-formula><graphic file="1029-242X-2011-592840-i174.gif"/></inline-formula>; that is, </p>
         <p>
            <display-formula id="M219">
               <graphic file="1029-242X-2011-592840-i175.gif"/>
            </display-formula>
         </p>
         <p>Let (<inline-formula><graphic file="1029-242X-2011-592840-i176.gif"/></inline-formula>) be double sequence of scalars such that <inline-formula><graphic file="1029-242X-2011-592840-i177.gif"/></inline-formula> for all <inline-formula><graphic file="1029-242X-2011-592840-i178.gif"/></inline-formula>. Then, the result follows from the following inequality: </p>
         <p>
            <display-formula id="M220">
               <graphic file="1029-242X-2011-592840-i179.gif"/>
            </display-formula>
         </p>
         <p>and this completes the proof.</p>
         <p>We have the following result in view of Remark 1.1 and Theorem 2.10.</p>
         <p>Corollary 2.11. </p>
         <p>The sequence space <inline-formula><graphic file="1029-242X-2011-592840-i180.gif"/></inline-formula> is monotone.</p>
         <p>Definition 2.12 (see [<abbr bid="B18">18</abbr>]). </p>
         <p>Let <inline-formula><graphic file="1029-242X-2011-592840-i181.gif"/></inline-formula> denote a four-dimensional summability method that maps the complex double sequences <inline-formula><graphic file="1029-242X-2011-592840-i182.gif"/></inline-formula> into the double-sequence <inline-formula><graphic file="1029-242X-2011-592840-i183.gif"/></inline-formula>, where the <inline-formula><graphic file="1029-242X-2011-592840-i184.gif"/></inline-formula>th term to <inline-formula><graphic file="1029-242X-2011-592840-i185.gif"/></inline-formula> is as follows: </p>
         <p>
            <display-formula id="M221">
               <graphic file="1029-242X-2011-592840-i186.gif"/>
            </display-formula>
         </p>
         <p/>
         <p>Such transformation is said to be nonnegative if <inline-formula><graphic file="1029-242X-2011-592840-i187.gif"/></inline-formula> is nonnegative for all <inline-formula><graphic file="1029-242X-2011-592840-i188.gif"/></inline-formula>, and <inline-formula><graphic file="1029-242X-2011-592840-i189.gif"/></inline-formula>.</p>
         <p>Definition 2.13. </p>
         <p>Let <inline-formula><graphic file="1029-242X-2011-592840-i190.gif"/></inline-formula> be a nonnegative matrix. Let <inline-formula><graphic file="1029-242X-2011-592840-i191.gif"/></inline-formula> be an Orlicz function and <inline-formula><graphic file="1029-242X-2011-592840-i192.gif"/></inline-formula> a factorable double sequence of strictly positive real numbers. Then, we define the following sequence spaces: </p>
         <p>
            <display-formula id="M222">
               <graphic file="1029-242X-2011-592840-i193.gif"/>
            </display-formula>
         </p>
         <p>for each <inline-formula><graphic file="1029-242X-2011-592840-i194.gif"/></inline-formula>. If <inline-formula><graphic file="1029-242X-2011-592840-i195.gif"/></inline-formula>, then we say <inline-formula><graphic file="1029-242X-2011-592840-i196.gif"/></inline-formula> is <inline-formula><graphic file="1029-242X-2011-592840-i197.gif"/></inline-formula> summable to <inline-formula><graphic file="1029-242X-2011-592840-i198.gif"/></inline-formula>, where <inline-formula><graphic file="1029-242X-2011-592840-i199.gif"/></inline-formula>. </p>
         <p>If we take <inline-formula><graphic file="1029-242X-2011-592840-i200.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i201.gif"/></inline-formula> for all <inline-formula><graphic file="1029-242X-2011-592840-i202.gif"/></inline-formula>, then we have </p>
         <p>
            <display-formula id="M223">
               <graphic file="1029-242X-2011-592840-i203.gif"/>
            </display-formula>
         </p>
         <p/>
         <p>Theorem 2.14. </p>
         <p><inline-formula><graphic file="1029-242X-2011-592840-i204.gif"/></inline-formula> is linear spaces.</p>
         <p>Proof. </p>
         <p>This can be proved by using the techniques similar to those used in Theorem 2.2.</p>
         <p>Theorem 2.15. </p>
         <p>(1) If <inline-formula><graphic file="1029-242X-2011-592840-i205.gif"/></inline-formula>, then </p>
         <p>
            <display-formula id="M224">
               <graphic file="1029-242X-2011-592840-i206.gif"/>
            </display-formula>
         </p>
         <p/>
         <p>(2) If <inline-formula><graphic file="1029-242X-2011-592840-i207.gif"/></inline-formula>, then </p>
         <p>
            <display-formula id="M225">
               <graphic file="1029-242X-2011-592840-i208.gif"/>
            </display-formula>
         </p>
         <p/>
         <p>Proof. </p>
         <p>(1) Let <inline-formula><graphic file="1029-242X-2011-592840-i209.gif"/></inline-formula>; since <inline-formula><graphic file="1029-242X-2011-592840-i210.gif"/></inline-formula>, we have </p>
         <p>
            <display-formula id="M226">
               <graphic file="1029-242X-2011-592840-i211.gif"/>
            </display-formula>
         </p>
         <p>and hence <inline-formula><graphic file="1029-242X-2011-592840-i212.gif"/></inline-formula>.</p>
         <p>(2) Let <inline-formula><graphic file="1029-242X-2011-592840-i213.gif"/></inline-formula> for each <inline-formula><graphic file="1029-242X-2011-592840-i214.gif"/></inline-formula> and <inline-formula><graphic file="1029-242X-2011-592840-i215.gif"/></inline-formula>. Let <inline-formula><graphic file="1029-242X-2011-592840-i216.gif"/></inline-formula>. </p>
         <p>Then, for each <inline-formula><graphic file="1029-242X-2011-592840-i217.gif"/></inline-formula>, there exists a positive integer <inline-formula><graphic file="1029-242X-2011-592840-i218.gif"/></inline-formula> such that </p>
         <p>
            <display-formula id="M227">
               <graphic file="1029-242X-2011-592840-i219.gif"/>
            </display-formula>
         </p>
         <p>for all <inline-formula><graphic file="1029-242X-2011-592840-i220.gif"/></inline-formula>. This implies that </p>
         <p>
            <display-formula id="M228">
               <graphic file="1029-242X-2011-592840-i221.gif"/>
            </display-formula>
         </p>
         <p>Thus, <inline-formula><graphic file="1029-242X-2011-592840-i222.gif"/></inline-formula>, and this completes the proof.</p>
      </sec>
   </bdy>
   <bm>
      <ack>
         <sec>
            <st>
               <p>Acknowledgments</p>
            </st>
            <p>The author wishes to thank the referees for their careful reading of the paper and for their helpful suggestions.</p>
         </sec>
      </ack>
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</art>