Transposition is Self-Inverse
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Theorem
All transpositions are self-inverse.
Proof
Let $\pi = \begin{bmatrix} k_1 & k_2 \end{bmatrix}$ be a transposition.
Writing $\pi \pi$ in cycle notation gives:
- $\begin{bmatrix} k_1 & k_2 \end{bmatrix} \begin{bmatrix} k_1 & k_2 \end{bmatrix}$
from which we see that $k_1 \to k_2 \to k_1$ and $k_2 \to k_1 \to k_2$.
The result follows from the definition of self-inverse.
$\blacksquare$