Cardinality of Set of All Mappings/Examples/2 Elements to 2 Elements

From ProofWiki
Jump to navigation Jump to search

Example of Cardinality of Set of All Mappings

Let $X = \set {a, b}$.

Let $Y = \set {u, v}$.

Then the mappings from $X$ to $Y$ are:

\(\text {(1)}: \quad\) \(\ds \map {f_1} a\) \(=\) \(\ds u\)
\(\ds \map {f_1} b\) \(=\) \(\ds v\)

\(\text {(2)}: \quad\) \(\ds \map {f_2} a\) \(=\) \(\ds u\)
\(\ds \map {f_2} b\) \(=\) \(\ds u\)

\(\text {(3)}: \quad\) \(\ds \map {f_3} a\) \(=\) \(\ds v\)
\(\ds \map {f_3} b\) \(=\) \(\ds v\)

\(\text {(4)}: \quad\) \(\ds \map {f_4} a\) \(=\) \(\ds v\)
\(\ds \map {f_4} b\) \(=\) \(\ds u\)

$f_1$ and $f_4$ are bijections.

$f_2$ and $f_3$ are neither surjections nor injections.