subset2

A is subset of B as <reln>

W3C sample WIRIS
A B
<math xmlns="http://www.w3.org/1998/Math/MathML">
  <reln>
    <subset/>
    <ci>A</ci>
    <ci>B</ci>
  </reln>
</math>

Author: Design Science, Inc. (E. Cannon, E. Tabacman, R.Miner)