Douglas Wilhelm Harder; Stan Devitt. <a href="http://www.w3.org/TR/2003/NOTE-mathml-units-20031110"><cite>Units in MathML.</cite></a> 10 November 2003. W3C Note. URL: <a href="http://www.w3.org/TR/2003/NOTE-mathml-units-20031110">http://www.w3.org/TR/2003/NOTE-mathml-units-20031110</a>