Tag: Abstract algebra
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This “argument” is famous for being used to prove the commutativity of the fundamental groups of H-spaces, hence the commutativity of higher homotopy groups.
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A memo on flatness and projectivity of modules.
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Salvaged from mathoverflow.
Often considered as “elementary” and overlooked, but requires a complete understanding of definitions.
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The following memo describes the subgroup structure of dihedral groups. As long as the site owner knows, no textbooks on abstract algebra (and general group theory, for that matter) discuss the subgroup structure. So this memo might be of some help to the students of mathematics. Caveat: the site owner no longer remembers where he got the information.
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MMM 