Let a and b belong to Sn. Prove that (a^-1)(b^-1)(a)(b) is an even permutation.

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Homework Help Overview

The problem involves proving that the expression (a^-1)(b^-1)(a)(b) is an even permutation, where a and b are elements of the symmetric group Sn. The discussion centers around the properties of permutations and their representations as products of cycles.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the definitions of even permutations and the representation of permutations as products of 2-cycles. There is a question about whether a^-1b^-1 can be expressed as a cycle and how many 2-cycles are needed to express a^-1.

Discussion Status

The discussion is ongoing, with participants seeking clarification on the definitions and implications of the properties of permutations. Some guidance has been offered regarding the relationship between a permutation and its inverse, but no consensus has been reached.

Contextual Notes

Participants are referencing definitions from their textbooks, and there is an acknowledgment of potential confusion due to external factors such as illness. The discussion reflects a need for deeper understanding of the concepts involved.

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Homework Statement


Let a and b belong to Sn. Prove that (a^-1)(b^-1)(a)(b) is an even permutation.


Homework Equations


Definitions I have are
Every permutation in Sn, n>1 is a product of 2 cycles
and
A permutation that can be expressed as a product of an even number of 2 cycles is called an even permutation

Thanks
 
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So, it appears you are saying that all the permutations involved in a^{-1}b^{-1}ab is a two-cycle and this is a product of 4 of them!
 
HallsofIvy said:
So, it appears you are saying that all the permutations involved in a^{-1}b^{-1}ab is a two-cycle and this is a product of 4 of them!
Maybe its my flu...but what do you mean exactly? What I said are two definitions out of the book.

Do I have to show that a^-1b^-1 is one cycle and that ab is another cycle?
 
If a can be expressed as a product of k 2-cycles, what can you say about how many 2-cycles it takes to express a-1?
 

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