Description: Define the value of an
operation.  Definition of operation value in
     [Enderton] p. 79.  Note that the syntax
is simply three class expressions
     in a row bracketed by parentheses.  There are no restrictions of any kind
     on what those class expressions may be, although only certain kinds of
     class expressions - a binary operation   and its arguments   and
      - will be useful
for proving meaningful theorems.  This definition
     is well-defined, although not very meaningful, when classes   and/or
       are proper
classes (i.e. are not sets).  On the other hand, we often
     find uses for this definition when   is a proper class.   is
     normally equal to a class of nested ordered pairs of the form defined by
     df-oprab 5529.  (Contributed by SF,
5-Jan-2015.) |