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[parent] symmetric group on three letters (Example)

This example is of the symmetric group on $ 3$ letters, usually denoted by $ S_3$. Here, we are considering the set of bijective functions on the set $ A=\{1,2,3\}$ which naturally arise as the set of permutations on $ A$. Our binary operation is function composition which results in a new bijective function. This example develops the multiplication table for $ S_3$. We start by listing the elements of our group. These elements are listed according to the second method as described in the entry on permutation notation.

$\displaystyle e={ 1\ 2\ 3 \choose 1\ 2\ 3} \hspace{20mm} r ={ 1\ 2\ 3 \choose 2\ 1\ 3}$
$\displaystyle a={ 1\ 2\ 3 \choose 2\ 3\ 1} \hspace{20mm} s ={ 1\ 2\ 3 \choose 3\ 2\ 1}$
$\displaystyle b={ 1\ 2\ 3 \choose 3\ 1\ 2} \hspace{20mm} t ={ 1\ 2\ 3 \choose 1\ 3\ 2}$

Here, our group is just $ S_3=\{e,a,b,r,s,t\}$. Now we can start to multiply and then fill in the table. First, we calculate the square of each element.

$\displaystyle a^2={ 1\ 2\ 3 \choose 2\ 3\ 1}{ 1\ 2\ 3 \choose 2\ 3\ 1}={ 1\ 2\ 3 \choose 3\ 1\ 2}= b$
$\displaystyle b^2={ 1\ 2\ 3 \choose 3\ 1\ 2}{ 1\ 2\ 3 \choose 3\ 1\ 2}={ 1\ 2\ 3 \choose 2\ 3\ 1}= a$
$\displaystyle r^2={ 1\ 2\ 3 \choose 2\ 1\ 3}{ 1\ 2\ 3 \choose 2\ 1\ 3}={ 1\ 2\ 3 \choose 1\ 2\ 3}=e$
$\displaystyle s^2={ 1\ 2\ 3 \choose 3\ 2\ 1}{ 1\ 2\ 3 \choose 3\ 2\ 1}={ 1\ 2\ 3 \choose 1\ 2\ 3}=e$
$\displaystyle t^2={ 1\ 2\ 3 \choose 1\ 3\ 2}{ 1\ 2\ 3 \choose 1\ 3\ 2}={ 1\ 2\ 3 \choose 1\ 2\ 3}=e$

Next, we will fill in the upper right $ 3\operatorname{x}3$ block, we only need $ ab$ and $ ba$ since we can use the fact that there can be no repetition in any row or column.

$\displaystyle ab ={ 1\ 2\ 3 \choose 2\ 3\ 1}{ 1\ 2\ 3 \choose 3\ 1\ 2}={ 1\ 2\ 3 \choose 1\ 2\ 3}=e$
$\displaystyle ba ={ 1\ 2\ 3 \choose 3\ 1\ 2}{ 1\ 2\ 3 \choose 2\ 3\ 1}={ 1\ 2\ 3 \choose 1\ 2\ 3}= e$

The other $ 3\operatorname{x}3$ blocks are also similar. Now continuing with the upper left 3 x 3 block, we go through the table again using the fact that there can be no repetition in any row or column.

$\displaystyle ar ={ 1\ 2\ 3 \choose 2\ 3\ 1}{ 1\ 2\ 3 \choose 2\ 1\ 3}={ 1\ 2\ 3 \choose 3\ 2\ 1}= s$
$\displaystyle as ={ 1\ 2\ 3 \choose 2\ 3\ 1}{ 1\ 2\ 3 \choose 3\ 2\ 1}={ 1\ 2\ 3 \choose 1\ 3\ 2}= t$

Similarly, we complete the final blocks of the table.

$\displaystyle ra ={ 1\ 2\ 3 \choose 2\ 1\ 3}{ 1\ 2\ 3 \choose 2\ 3\ 1}={ 1\ 2\ 3 \choose 1\ 3\ 2}= t$
$\displaystyle rb ={ 1\ 2\ 3 \choose 2\ 1\ 3}{ 1\ 2\ 3 \choose 3\ 1\ 2}={ 1\ 2\ 3 \choose 3\ 2\ 1}= s$

$\displaystyle sa ={ 1\ 2\ 3 \choose 3\ 2\ 1}{ 1\ 2\ 3 \choose 2\ 3\ 1}={ 1\ 2\ 3 \choose 2\ 1\ 3}= r$
$\displaystyle sr ={ 1\ 2\ 3 \choose 3\ 2\ 1}{ 1\ 2\ 3 \choose 2\ 1\ 3}={ 1\ 2\ 3 \choose 2\ 3\ 1}= a$

Finally, we fill in the table using the calculated values above.

\begin{displaymath}\begin{array}{\vert c\vert\vert c\vert c\vert c\vert c\vert c... ...& b \ \hline t & t & s & r & b & a & e \ \hline \end{array}\end{displaymath}



"symmetric group on three letters" is owned by Wkbj79. [ full author list (2) | owner history (1) ]
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Cross-references: column, row, square, permutation notation, group, composition, function, binary operation, permutations, bijective functions, symmetric group
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This is version 10 of symmetric group on three letters, born on 2006-04-25, modified 2007-08-08.
Object id is 7870, canonical name is Example20of20symmetric20group.
Accessed 1286 times total.

Classification:
AMS MSC20B30 (Group theory and generalizations :: Permutation groups :: Symmetric groups)

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