The Fortress Language Specification - CiteSeerX

24.2.5 opr ∨(self,other: BooleanInterval): BooleanInterval
24.2.6 opr ⊕(self,other: BooleanInterval):BooleanInterval
The logical exclusive OR operator ∨ ( XOR ) returns Impossible if either argument is Impossible; otherwise it returns
Uncertain if either argument is Uncertain; otherwise it returns False if the arguments are strictly equivalent;
otherwise it returns True. It obeys the interval containment rule.
The operator ⊕ ( OPLUS ) does the same thing as ∨ . The ∨ or ⊕ operator may be described by this table:
∨ or ⊕ Uncertain True False Impossible
Uncertain Uncertain Uncertain Uncertain Impossible
True Uncertain False True Impossible
False Uncertain True False Impossible
Impossible Impossible Impossible Impossible Impossible
24.2.7 opr ≡(self,other: BooleanInterval):BooleanInterval
24.2.8 opr =(self,other: BooleanInterval):BooleanInterval
24.2.9 opr ↔(self,other: BooleanInterval):BooleanInterval
The logical equivalence, or exclusive NOR, operator ≡ ( EQV ) returns Impossible if either argument is Impossible;
otherwise it returns Uncertain if either argument is Uncertain; otherwise it returns True if the arguments are strictly
equivalent; otherwise it returns False. It obeys the interval containment rule. (Thus its behavior on boolean interval
values is not the same as that of the strict equivalence operator = .)
The equality operator = and the if-and-only-if operator ↔ ( IFF ) do the same thing as ≡ . The ≡ or = or ↔
operator may be described by this table:
≡ or = or ↔ Uncertain True False Impossible
Uncertain Uncertain Uncertain Uncertain Impossible
True Uncertain True False Impossible
False Uncertain False True Impossible
Impossible Impossible Impossible Impossible Impossible
24.2.10 opr →(self,other: BooleanInterval):BooleanInterval
The logical implication operator → ( IMPLIES ) returns Impossible if either argument is Impossible; otherwise it
returns True if the first argument is False or the second argument is True; otherwise it returns Uncertain if either
argument is Uncertain; otherwise it returns False. It obeys the interval containment rule. The → operator may be
described by this table:
→ Uncertain True False Impossible
Uncertain Uncertain True Uncertain Impossible
True Uncertain True False Impossible
False True True True Impossible
Impossible Impossible Impossible Impossible Impossible
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