If a transformation maps [tex] a \mapsto b [/tex], then [tex] b [/tex] is the image of [tex] a [/tex], and [tex] a [/tex] is the preimage of [tex] b[/tex]. So,
- the image of [tex] a [/tex] is [tex] b [/tex]
- the preimage of [tex] b [/tex] is [tex] a [/tex]
- the image of [tex] c [/tex] is [tex] d [/tex]
- the preimage of [tex] d [/tex] is [tex] c [/tex]