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The Fortress Language Specification - CiteSeerX

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24.1.20 getter hashCode(): N64<br />

24.1.21 toString():String<br />

<strong>The</strong> toString method returns either true or false as appropriate.<br />

24.2 <strong>The</strong> Trait <strong>Fortress</strong>.Standard.BooleanInterval<br />

A boolean interval is a set of boolean values. <strong>The</strong>re are two distinct boolean values, true and false , and therefore<br />

there are four distinct boolean intervals, which for convenience are given names:<br />

True = {true}<br />

False = {false}<br />

Uncertain = {true,false}<br />

Impossible = { }<br />

Logical operations on intervals obey the interval containment rule: the result interval must contain every boolean result<br />

that can be produced by applying the operator to a boolean value taken from each argument interval. For example, if<br />

P and Q are boolean intervals, then by definition P ∧ Q = { x ∧ y | x ← P, y ← Q } .<br />

A principal application of boolean intervals is to express the results of numerical comparison of numerical intervals.<br />

In this way numerical comparisons can also obey the interval containment rule.<br />

Set operations such as ∪ and ∩ may also be used on boolean intervals.<br />

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