The Fortress Language Specification - CiteSeerX

24.2.11 opr ∧(self,other: BooleanInterval): BooleanInterval
The logical NAND (NOT AND) operator ∧ ( NAND ) returns Impossible if either argument is Impossible; otherwise it
returns True if either argument is False; 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 Uncertain True Impossible
True Uncertain False True Impossible
False True True True Impossible
Impossible Impossible Impossible Impossible Impossible
24.2.12 opr ∨(self,other: BooleanInterval): BooleanInterval
The logical NOR (NOT OR) operator ∨ ( NOR ) returns Impossible if either argument is Impossible; otherwise it
returns False if either argument is True; otherwise it returns Uncertain if either argument is Uncertain; otherwise
it returns True. It obeys the interval containment rule. The ∨ operator may be described by this table:
∨ Uncertain True False Impossible
Uncertain Uncertain False Uncertain Impossible
True False False False Impossible
False Uncertain False True Impossible
Impossible Impossible Impossible Impossible Impossible
24.2.13 opr ∈(other: Boolean,self):Boolean
The operator ∈ ( IN ) returns true if its first argument, a boolean value, is contained in its second argument, a boolean
interval regarded as a set; otherwise it returns false . The ∈ operator may be described by this table:
∈ Uncertain True False Impossible
true true true false false
false true false true false
24.2.14 opr ∩(self,other: BooleanInterval): BooleanInterval
The intersection operator ∩ ( INTERSECTION or CAP ) returns Impossible if either argument is Impossible; otherwise,
if either argument is Uncertain, it returns the other argument; otherwise, if the arguments are the same value
(strictly equivalent), it returns that value; otherwise it returns Impossible. The ∩ operator may be described by this
table:
∩ Uncertain True False Impossible
Uncertain Uncertain True False Impossible
True True True Impossible Impossible
False False Impossible False Impossible
Impossible Impossible Impossible Impossible Impossible
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