<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; ">Using the MakeIndex package to create an index, I wanted to have an entry, as if it were an ordinary R, but printed as a blackboard bold R. The following indexing entry in the text<DIV> \index{R@$\mathbb{R}$}</DIV><DIV>(following the rules on p. 652 of the Latex Companion, 2nd ed.) was rejected. Here is the</DIV><DIV>entry from the ilg file:</DIV><DIV> !! Input index error (file = Calculus.idx, line = 32):<DIV> -- Extra `@' at position 5 of first argument.</DIV>The line referred to in the idx file is</DIV><DIV> \indexentry{R@$\@mathbb {R}$}{17}</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>So the program itself seems to add an extra @, which creates an error. How do I avoid the </DIV><DIV>problem?<BR><DIV> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Zbigniew Nitecki</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Department of Mathematics</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Tufts University</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Medford, MA 02155</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">telephones:</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Office<SPAN class="Apple-converted-space"><SPAN class="Apple-converted-tab"> </SPAN></SPAN>(617)627-3843</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Dept.<SPAN class="Apple-converted-space"><SPAN class="Apple-converted-tab"> </SPAN></SPAN>(617)627-3234</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Dept. fax<SPAN class="Apple-converted-space"><SPAN class="Apple-converted-tab"> </SPAN></SPAN>(617)627-3966</FONT></P> </DIV><BR></DIV></BODY></HTML>