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The implementor must ensure sgn(x.compareTo(y) for all x and y. (This implies that 
) == -sgn(y.compareTo
(x))x.compareTo must throw an exception iff (y)y.compareTo throws an exception.)(x)
The implementor must also ensure that the relation is transitive: (x.compareTo implies >0 && y.compareTo(z)>0)x.compareTo(z)>0.
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