rec-prsubset1

A is proper subset of B as <apply>

W3C sample	WIRIS
	$A B$

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <apply>
    <prsubset/>
    <ci>A</ci>
    <ci>B</ci>
  </apply>
</math>

Author: MathML 2 Recommendation