such that
is always equivalent to "
is
." This is obviously extensional. It is equivalent to the assertion that the class defined by the function
is a unit class, i.e. a class having one member; in other words, a class which is a member of 1.
such that
is always equivalent to "
is
." This is obviously extensional. It is equivalent to the assertion that the class defined by the function
is a unit class, i.e. a class having one member; in other words, a class which is a member of 1.