/ GENTLE PRIMER
/ A Summary of Predefined Predicates
The Predicates eq, ne, lt, le, ge, gt
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.
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