Abstract Algebra: Subgroup Proof

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SUMMARY

In the discussion, participants analyze the proof that if H is a subgroup of G and K is a subgroup of H, then K is also a subgroup of G. The key points established are that K must contain the identity element of H and G, and that every element of K is also an element of H, which in turn is an element of G. The proof hinges on the definitions of subgroups, specifically the requirements of non-emptiness, closure under multiplication, and the existence of inverses.

PREREQUISITES
  • Understanding of subgroup definitions in group theory
  • Familiarity with group operations and properties
  • Knowledge of identity elements in algebraic structures
  • Basic proof techniques in abstract algebra
NEXT STEPS
  • Study the properties of subgroups in group theory
  • Learn about the concept of normal subgroups and their significance
  • Explore the implications of Lagrange's theorem in group theory
  • Investigate examples of groups and their subgroups, such as cyclic groups
USEFUL FOR

This discussion is beneficial for students of abstract algebra, particularly those studying group theory, as well as educators seeking to clarify subgroup relationships and proof techniques.

schmitty10
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Homework Statement


Show that if H is a subgroup of G and K is a subgroup of H, then K is a subgroup of G.


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The Attempt at a Solution


Well I know that H is a subgroup of G if H is non empty, has multiplication, and his inverses. So I assume that K is a subgroup of H for those same reasons, but I'm unsure how to show K is a subgroup of G based on those two results. I'm looking for the connection. Please help. Thank you.
 
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You might be confused because there is not much to show. K is a group in itself. So it has multiplication, inverses and an identity all by itself. I think all you really have to show is that the identity element in K is the same as the identity element in H and G. And, of course, that every element in K is also in H and hence in G. But that's easy.
 
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