Membership in the inverse of a class relation and in the preimage of a class, the preimage and the image under a map between classes, and enlarging the codomain of a map.
In the setting of Class Theory NBG: the Axioms, Standing Conventions and Basic Notation, let , , , , and be classes, not necessarily sets. is the inverse of , is the image of under , and is the preimage of under .
For all sets and : if and only if .
For every set : if and only if there is a set with and .
If is a map, then for every set : if and only if and , where is the value of at .
If is a map, then .
If is a map and for every , then is a map.
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