Definition:Preimage/Mapping/Subset

Definition
Let $f: S \to T$ be a mapping.

Let $f^{-1} \subseteq T \times S$ be the inverse of $f$, defined as:


 * $f^{-1} = \set {\tuple {t, s}: f \paren s = t}$

Let $Y \subseteq T$.

The preimage of $Y$ under $f$ is defined as:


 * $f^{-1} \left [{Y}\right] := \set {s \in S: \exists y \in Y: f \paren s = y}$

That is, the preimage of $Y$ under $f$ is the image of $Y$ under $f^{-1}$, where $f^{-1}$ can be considered as a relation.

If no element of $Y$ has a preimage, then $f^{-1} \left [{Y}\right] = \varnothing$.

Also known as
Some sources use counter image or inverse image instead of preimage.

Also denoted as
When the language of induced mappings is used, then $f^\gets \paren Y$ is seen for $f^{-1} \left [{Y}\right]$.

Also see

 * Definition:Image of Subset under Mapping
 * Definition:Preimage Mapping
 * Definition:Domain of Mapping
 * Definition:Codomain of Mapping
 * Definition:Range
 * Preimage of Subset under Mapping equals Union of Preimages of Elements

Generalization

 * Definition:Preimage of Relation