Cardinality <i>is</i> the number of elements in a set.<p>If every element in set A is in set B, and there are elements in set A left over it&#x27;s larger because that&#x27;s what larger means.  {A,B} &lt; {A,B,C}<p>There are countable and uncountable infinite set&#x27;s.  All countable set&#x27;s have a bijection with N. However, there are more than two sizes of infinite sets.  Real numbers &lt; Imaginary numbers.