Description: Define the image of a class (as restricted by another class).
Definition 6.6(2) of TakeutiZaring p. 24. For example,
( F = { <. 2 , 6 >. , <. 3 , 9 >. } /\ B = { 1 , 2 } )-> ( F " B ) = { 6 } ( ex-ima ). Contrast with restriction
( df-res ) and range ( df-rn ). For an alternate definition, see
dfima2 . (Contributed by NM, 2-Aug-1994)