For a bijection f from X to Y with inverse g and a subset E of X, the image f[E] is the preimage of E under g, and the preimage of f[E] under f is E.
In the setting of Routine Facts Used Without Citation: Arithmetic, Maps, Predicativity and Indices, let and be sets, let be a bijection, let be its inverse, and let . Images and preimages are as in The Image and the Preimage of a Class under a Class (i) and The Image and the Preimage of a Class under a Class (ii).
The image under is the preimage under .
The preimage of the image is the set itself.
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