<document type=raw>
<c-nonum><h4>The equivalence relation <em> - congruence</em></h4></c-nonum> <!--> <ul> <li>x = x <li>x = y = > y = x <li>x = y / y = z = > x = z <li>x = y = > f(...,x,...) = f(...,y,...) </ul> <h4>Equivalence classes <em> - representatives</em></h4> <!--> <ul><li> abstract elements <em> - GUT / = </em></ul> <!--> </document>