Bijection/Examples/n+1 Mapping on Integers
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Example of Bijection
Let $f: \Z \to \Z$ be the mapping defined on the set of integers as:
- $\forall n \in \Z: \map f n = n + 1$
Then $f$ is a bijection.
Proof
Let $n_1$ and $n_2$ be integers.
Then:
\(\ds \map f {n_1}\) | \(=\) | \(\ds \map f {n_2}\) | by supposition | |||||||||||
\(\ds \leadsto \ \ \) | \(\ds n_1 + 1\) | \(=\) | \(\ds n_2 + 1\) | Definition of $f$ | ||||||||||
\(\ds \leadsto \ \ \) | \(\ds n_1\) | \(=\) | \(\ds n_2\) |
Hence by definition $f$ is an injection.
$\Box$
Let $m \in \Z$.
Let $n = m - 1$.
We have that:
- $n \in \Z$
and:
- $\map f n = m$
Hence by definition $f$ is a surjection.
$\Box$
Thus $f$ is both an injection and a surjection, and so a bijection
$\blacksquare$
Sources
- 1975: T.S. Blyth: Set Theory and Abstract Algebra ... (previous) ... (next): $\S 5$. Induced mappings; composition; injections; surjections; bijections