<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE article  PUBLIC "-//NLM//DTD Journal Publishing DTD v3.0 20080202//EN" "http://dtd.nlm.nih.gov/publishing/3.0/journalpublishing3.dtd"><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" dtd-version="3.0" xml:lang="en" article-type="research article"><front><journal-meta><journal-id journal-id-type="publisher-id">JMF</journal-id><journal-title-group><journal-title>Journal of Mathematical Finance</journal-title></journal-title-group><issn pub-type="epub">2162-2434</issn><publisher><publisher-name>Scientific Research Publishing</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.4236/jmf.2014.42008</article-id><article-id pub-id-type="publisher-id">JMF-43032</article-id><article-categories><subj-group subj-group-type="heading"><subject>Articles</subject></subj-group><subj-group subj-group-type="Discipline-v2"><subject>Business&amp;Economics</subject><subject> Physics&amp;Mathematics</subject></subj-group></article-categories><title-group><article-title>
 
 
  On Local Times: Application to Pricing Using Bid-Ask
 
</article-title></title-group><contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>aul</surname><given-names>C. Kettler</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref><xref ref-type="corresp" rid="cor1"><sup>*</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Olivier</surname><given-names>Menoukeu-Pamen</given-names></name><xref ref-type="aff" rid="aff2"><sup>2</sup></xref><xref ref-type="corresp" rid="cor1"><sup>*</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Frank</surname><given-names>Proske</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref><xref ref-type="corresp" rid="cor1"><sup>*</sup></xref></contrib></contrib-group><aff id="aff2"><addr-line>Institute for Financial and Actuarial Mathematics, Department of Mathematics, University of Liverpool, Liverpool, UK</addr-line></aff><aff id="aff1"><addr-line>Centre of Mathematics for Applications, Department of Mathematics, University of Oslo, Oslo, Norway</addr-line></aff><author-notes><corresp id="cor1">* E-mail:<email>paulck@math.uio.no(ACK)</email>;<email>Menoukeu@liverpool.ac.uk(OM)</email>;<email>proske@math.uio.no(FP)</email>;</corresp></author-notes><pub-date pub-type="epub"><day>14</day><month>02</month><year>2014</year></pub-date><volume>04</volume><issue>02</issue><fpage>84</fpage><lpage>94</lpage><history><date date-type="received"><day>October</day>	<month>12,</month>	<year>2013</year></date><date date-type="rev-recd"><day>December</day>	<month>3,</month>	<year>2013</year>	</date><date date-type="accepted"><day>January</day>	<month>4,</month>	<year>2014</year></date></history><permissions><copyright-statement>&#169; Copyright  2014 by authors and Scientific Research Publishing Inc. </copyright-statement><copyright-year>2014</copyright-year><license><license-p>This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/</license-p></license></permissions><abstract><p>
 
 
   In this paper, we derive the evolution of a stock price from the dynamics of the “best bid” and “best ask”. Under the assumption that the bid and ask prices are described by semimartingales, we study the completeness and the possibility for arbitrage on such a market. Further, we discuss (insider) hedging for contingent claims with respect to the stock price process.  
    
 
</p></abstract><kwd-group><kwd>Order Statistics; Semimartingales; Local Times; Arbitrage</kwd></kwd-group></article-meta></front><body><sec id="s1"><title>NOTES</title><disp-formula id="scirp.43032-formula75166"><graphic  xlink:href="http://html.scirp.org/file/3-1490224x131.png"  xlink:type="simple"/></disp-formula><p><sup>1</sup>In fact since S is continuous and since all continuous sigma martingales are in fact local martingales, we only need to concern ourselves with local martingales</p></sec></body><back><ref-list><title>References</title><ref id="scirp.43032-ref1"><label>1</label><mixed-citation publication-type="other" xlink:type="simple">J. Harrison and D. Kreps, “Martingales and Arbitrage in Multiperiod Securities Markets,” Journal of Economic Theory, Vol. 20, No. 3, 1979, pp. 381-408. http://dx.doi.org/10.1016/0022-0531(79)90043-7</mixed-citation></ref><ref id="scirp.43032-ref2"><label>2</label><mixed-citation publication-type="other" xlink:type="simple">J. Harrison and S. 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