Log Message: 
Added methods for testing containment of one set in another, and so
on. These include:
$A>contains($B) Test if $B is a subset of $A (or an
element of $A if $B$ is a real number).
$A>isSubsetOf($B) Test if $A is a subset of $B.
$A>isEmpty True if $A is the empty set.
$A>intersects($B) True if $A and $B have numbers in common.
$A>intersect($B) The set of numbers common to both $A and $B.
Be careful of the difference between "intersect" and "intersects".
One is a set the other a true/false value.
