Cartesian Product of Permutations?

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SUMMARY

The discussion centers on the isomorphism between groups, specifically examining whether G is isomorphic to the Cartesian product H × G/H, using G = S_3 and its subgroup H = A_3 as examples. The quotient group G/H consists of cosets of H, which in this case is isomorphic to the two-element group {1, -1}, representing the parity of permutations. The multiplication of elements in the Cartesian product A_3 × (S_3/A_3) is demonstrated with the example of combining permutations and their corresponding parity.

PREREQUISITES
  • Understanding of group theory concepts, specifically isomorphisms and quotient groups.
  • Familiarity with symmetric groups, particularly S_3 and alternating groups like A_3.
  • Knowledge of permutation multiplication and parity in the context of group operations.
  • Basic grasp of Cartesian products in set theory.
NEXT STEPS
  • Study the properties of symmetric groups, focusing on S_3 and its subgroups.
  • Learn about quotient groups and their applications in group theory.
  • Explore the concept of group isomorphism in greater detail.
  • Investigate the role of parity in permutations and its implications in group operations.
USEFUL FOR

Mathematicians, students of abstract algebra, and anyone interested in advanced group theory concepts, particularly those involving permutations and isomorphisms.

Parmenides
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Suppose I was asked if [itex]G \cong H \times G/H[/itex]. At first I considered a familiar group, [itex]G = S_3[/itex] with its subgroup [itex]H = A_3[/itex]. I know that the quotient group is the cosets of [itex]H[/itex], but then I realized that I have no idea how to interpret a Cartesian product of any type of set with elements that aren't just numbers. An ordered pair of permutations doesn't make sense (this is not a homework question). I'd be grateful for some clarity.
 
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If G1 and G2 are groups, then
[tex]G_1 \times G_2 = \{ (g_1,g_2)\ :\ g_1 \in G_1,\ g_2\in G_2 \}[/tex]
with the multiplication
[tex](g_1,g_2)\cdot (h_1,h_2) = (g_1 h_1, g_2 h_2)[/tex].

So if you have G = S3, and H = A3, G/H is isomorphic to the two element group {1,-1} (where each permutation gets mapped to its parity), and a general element of A3 x (S3/A3) is [itex](\sigma, \pm 1 )[/itex] where sigma here is any even permutation.

For example,
[tex]\left( (1 2 3 ),-1 \right) \cdot \left( (1 2 3), 1 \right) = \left( (1 3 2), -1 \right)[/tex]
is a multiplication inside of this group.
 

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