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The Predicates eq, ne, lt, le, ge, gt
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The conditions eq and ne are used to compare values for equality. 

   eq(X, Y)
succeeds if X is equal to Y and fails otherwise. 

   ne(X, Y)
succeeds if X is not equal to Y and fails otherwise. These predicates work for all types including user-defined types, i.e. they may be used to compare terms. For example, 

   eq(list(red, X), list(red, list(yellow,nil)))
succeeds if X is list(yellow,nil).

The predicates gt, ge, lt, and le are defined only for the types INT and STRING. 


   gt(X, Y)
succeeds if X is greater than Y and fails otherwise.

For example, 


   gt(N, 0)
succeeds if N is a positive number.

In the case of strings, the lexicographical order is used for comparison. For example, 


   gt("axy", "abc")
   gt("aaaa", "aa")
succeed.

Similarly, ge, lt, and le stand for ``greater or equal'', ``less than'', and ``less or equal'', respectively





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