Proving the Inclusion of <a> in H: A Permutation Group Proof

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SUMMARY

The discussion centers on proving the inclusion of an element \( a \) in a subgroup \( H \) of a group \( G \). The proof establishes that \( a \) is in \( H \) if and only if the set generated by \( a \), denoted as \( \langle a \rangle \), is a subset of \( H \). The proof is structured in two parts: first, showing that if \( a \) is in \( H \), then \( \langle a \rangle \) is a subset of \( H \); second, demonstrating that if \( \langle a \rangle \) is a subset of \( H \), then \( a \) must be in \( H \). The proof is complete and correctly follows group theory principles.

PREREQUISITES
  • Understanding of group theory concepts, specifically subgroups and generated sets.
  • Familiarity with notation such as \( \langle a \rangle \) for generated sets.
  • Knowledge of group properties, including closure and the existence of inverses.
  • Basic proof techniques in mathematics, particularly direct proof methods.
NEXT STEPS
  • Study the properties of subgroups in group theory.
  • Learn about the concept of generated sets and their significance in abstract algebra.
  • Explore advanced topics in group theory, such as normal subgroups and quotient groups.
  • Review proof strategies in mathematics to strengthen logical reasoning skills.
USEFUL FOR

This discussion is beneficial for students of abstract algebra, particularly those studying group theory, as well as educators looking for clear examples of subgroup proofs.

iamalexalright
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Homework Statement


Suppose G is a group, H < G (H is a subgroup of G), and a is in G.

Prove that a is in H iff <a> is a subset of H.


Homework Equations


<a> is the set generated by a (a,aa,aa^-1,etc)


The Attempt at a Solution


For some reason this seems too easy:

1. Suppose a is in H.
Since H is a group, a^-1 is in H.
Since H is a group aa, is in H (as is aa^-1, etc.)
Thus <a> is a subset of H.

2. Suppose <a> is a subset of H.
Obviously a is in H.

And this completes the proof... or am I missing something?
 
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