|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 10723 (−) to prevent
syntax ambiguity. For example, looking at the
syntax definition co 7023, if we used the same symbol
then "( − 𝐴 − 𝐵) " could mean either
"− 𝐴 " minus "𝐵",
it could represent the (meaningless) operation of
classes "− " and "− 𝐵
" connected with "operation" "𝐴".
On the other hand, "(-𝐴 − 𝐵) " is