**Description: **Extend class notation to
include unary minus. The symbol - is not a
class by itself but part of a compound class definition. We do this
rather than making it a formal function since it is so commonly used.
Note: We use different symbols for unary minus (-) and subtraction
cmin 6959 (−) to prevent
syntax ambiguity. For example, looking at the
syntax definition co 5455, if we used the same symbol
then "( − *A* − *B*) " could mean either "− *A* " minus
"*B*", or
it could represent the (meaningless) operation of
classes "− " and "− *B* "
connected with "operation" "*A*".
On the other hand, "(-*A* − *B*) " is
unambiguous. |