| 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 8197 (−) to prevent
syntax ambiguity.  For example, looking at the
     syntax definition co 5922, 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. |