5.2.2 Equation numbers

A tricky point is equation labelling and numbering. tbook supports three ways of giving an equation a label:

1. A <math> element has an id attribute. For example:

             <math id="Einstein">
               <mi>E</mi>
               <mo>=</mo>
               <mi>m</mi>
               <msup>
                 <mi>c</mi>
                 <mn>2</mn>
               </msup>
             </math>
        

   or simply

             <dm id="Einstein">E=mc^2</dm>
        

   You can refer to it with

             <p>The <ref refid="Einstein">equation</ref> is the famous energy
               equivalence.</p>
        

2. An <mtd> element with an id within an equation array:

             <math>
               <mtable groupalign="right center left">
                 <mtr>
                   <mtd id="equation1"> <m> 1+1 #=# 2 </m> </mtd>
                   <mtd> <m> 4 #=# 2 &CenterDot; 2 </m> </mtd>
                 </mtr>
               </mtable>
             </math>
        

   which you can refer to by saying

             <p>If you want to see a pretty useless equation have a look at
               <ref refid="equation1">equation</ref>.</p>
        

3. An <mlabeledtr> element with an id within an equation array, and the contents of the first <mtd> element of such an <mlabeledtr> row. This version is pretty obscure, and you cannot refer to it with <ref> but only with <mathref>.

I would recommend you to use only 1. and 2.