The Fortress Language Specification - CiteSeerX

24.2.15 opr ∪(self,other: BooleanInterval): BooleanInterval
The union operator ∪ ( UNION or CUP ) returns Uncertain if either argument is Uncertain; otherwise, if either argument
is Impossible, it returns the other argument; otherwise, if the arguments are the same value (strictly equivalent),
it returns that value; otherwise it returns Uncertain. The ∪ operator may be described by this table:
∪ Uncertain True False Impossible
Uncertain Uncertain Uncertain Uncertain Uncertain
True Uncertain True Uncertain True
False Uncertain Uncertain False False
Impossible Uncertain True False Impossible
24.2.16 opr SET COMPLEMENT(self):BooleanInterval
The set complement operator SET COMPLEMENT returns Uncertain if its argument is Impossible, Impossible if its
argument is Uncertain, False if its argument is True, and True if its argument is False.
24.2.17 opr SYMDIFF(self,other: BooleanInterval):BooleanInterval
The symmetric difference operator SYMDIFF produces a result that contains a given boolean value if and only if
exactly one of the arguments contains that boolean value. The SYMDIFF operator may be described by this table:
SYMDIFF Uncertain True False Impossible
Uncertain Impossible False True Uncertain
True False Impossible Uncertain True
False True Uncertain Impossible False
Impossible Uncertain True False Impossible
24.2.18 opr \(self,other: BooleanInterval):BooleanInterval
The set difference operator \ ( SETMINUS ) produces a result that contains a given boolean value if and only if the
first argument contains that boolean value but the second argument does not. The \ operator may be described by this
table:
\ Uncertain True False Impossible
Uncertain Impossible False True Uncertain
True Impossible Impossible True True
False Impossible False Impossible False
Impossible Impossible Impossible Impossible Impossible
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