|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 6979 (−) 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
it could represent the (meaningless) operation of
classes "− " and "− B "
connected with "operation" "A".
On the other hand, "(-A − B) " is