 constraints
that are involved in the following types of situations:

1.  Distinction:     A =/= B
    Also known as:   logical inequality, exclusive disjunction
    Represented as:  ( A , B )
    Graphed as:
    |
    |   A   B
    |   o---o
    |    \ /
    |     @

2.  Equality:        A = B
    Also known as:   logical equivalence, if and only if, A &lt;=&gt; B
    Represented as:  (( A , B ))
    Graphed as:
    |
    |   A   B
    |   o---o
    |    \ /
    |     o
    |     |
    |     @

3.  Implica