Description: Define the range of a class. For example,
F = { <. 2 , 6 >. , <. 3 , 9 >. } -> ran F = { 6 , 9 } ( ex-rn ).
Contrast with domain (defined in df-dm ). For alternate definitions,
see dfrn2 , dfrn3 , and dfrn4 . The notation " ran " is used
by Enderton. The range of a function is often also called "the image of
the function" (see definition in Lang p. ix), which can be justified
by imadmrn . Not to be confused with "codomain" (see df-f ), which
may be a superset/superclass of the range (see frn ). (Contributed by NM, 1-Aug-1994)