<?xml version="1.0"?> <!DOCTYPE para PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"> <para> The equation <informalequation><alt>e^(pi*i) + 1 = 0</alt><graphic fileref="figures/epi10"/></informalequation> is delightful because it joins together five of the most important mathematical constants. </para>