express a set of equations

Hi all,

In MathML, how can I express a set of equations?
Is following MathML correct to express two equations? 
or is there any parent element that can have those two 'reln' elements as a child?

N = a + b
M = c + d

<reln>
   <eq/>
   <ci>N</ci>
   <apply>
      <plus/>
      <ci>a</ci>
      <ci>b</ci>
   </apply>
</reln>
<reln>
   <eq/>
   <ci>M</ci>
   <apply>
      <plus/>
      <ci>c</ci>
      <ci>d</ci>
   </apply>
</reln>


Thanks in advance.