#\ C True if the constraint C is false.
C1 #/\ C2 True if both of the constraints C1 and
C2 are true. This goal is equivalent to (C1,C2).
C1 #\/ C2 True if either C1 or C2 is true.
This goal is equivalent to (C1;C2) but does not create choice
points.
C1 #=> C2 If C1 is true, then C2 is also
true.
C1 #<=> C2 C1 and C2 are equivalent.
C1 #\ C2 True if exactly one of C1 and C2 is
true.