Prove H Contains in gH ≠ g-H: Counting Principles

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SUMMARY

The discussion focuses on proving that if H is a subgroup of G and for any elements a and b in G, aH is not equal to bH, then gH is not equal to g^-1H for all g in G. The participants explore the implications of this condition, particularly in relation to normal subgroups. The example provided, where G is the symmetric group Sym(3) and H is the subgroup {1, (12)}, illustrates the concepts effectively.

PREREQUISITES
  • Understanding of group theory concepts, specifically subgroups and cosets.
  • Familiarity with normal subgroups and their properties.
  • Knowledge of symmetric groups, particularly Sym(3).
  • Basic proficiency in mathematical proofs and contrapositive reasoning.
NEXT STEPS
  • Study the properties of normal subgroups in group theory.
  • Learn about cosets and their significance in group structures.
  • Explore examples of symmetric groups and their subgroup structures.
  • Investigate the contrapositive method in mathematical proofs for deeper understanding.
USEFUL FOR

This discussion is beneficial for students of abstract algebra, mathematicians focusing on group theory, and anyone interested in the properties of subgroups and their applications in various mathematical contexts.

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Homework Statement


Suppose that H is a subgroup of G such that whenever H a is not equal to H b.
Then a H not equal to b H.
Prove that g H g ^-H
Contains H.
For all g Is an element of G.[/B]

Homework Equations

The Attempt at a Solution


I tried the contrapositive position
( sorry, I'm doing this on an iPhone and I can't access latex )
 
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Are you sure you haven't a mistake in there? ##H \subseteq gHg^{-1}H## for all ##g\in G## means, ##H \trianglelefteq G## is a normal subgroup. What about ##G=Sym (3) = \{1,(12),(13),(23),(123),(132)\}## and ##H=\{1,(12)\}##?
 

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