next up previous
Next: aa_solns_7 Up: aa_solns_7 Previous: aa_solns_7



For Problem V-11:

Starting from the right, $ 1 \mapsto 2 \mapsto 3, 2 \mapsto 1
\mapsto 2, 3 \mapsto 3 \mapsto 1$, so the answer is $ \left(\begin{array}{ccc}1&2&3\\  3&2&1\end{array}\right)$.



For Problem V-12: $ (12)(23) = (123)$ since going right to left, $ 1 \mapsto 1 \mapsto 2,
2 \mapsto 3 \mapsto 3, 3 \mapsto 2 \mapsto 1$. $ (23)(12) = (132)$ since $ 1 \mapsto 2 \mapsto 3, 3 \mapsto 3 \mapsto 2, 2 \mapsto 1 \mapsto
1$. Therefore they do not commute.

Since the particular symbols do not really matter and since $ (ab) = (ba)$, we see that two transpositions that have just one symbol in common do not commute; instead their products are give distinct 3-cycles.



For Problem V-13:

(This problem had a misprint: the last 4 should be 1.)

$ 1 \mapsto 2 \mapsto 4 \mapsto 7 \mapsto 1$, $ 3 \mapsto 3$, and $ 5 \mapsto 6 \mapsto 5$, so the ``cycle decomposition'' is $ (1247)(56)$.



For Problem V-14: \begin{displaymath}
\begin{array}{c\vert cccccc}
& \mathbf{1}& (123) & (132) & ...
...(23) & (13) & (12) & (132) & (123) & \mathbf{1}\\
\end{array}\end{displaymath}

Note: For $ S_4$ the table would be $ 24 \times 24$, and some elements would be non-cycles such as $ (12)(34)$.



Kirby A. Baker 2001-11-19