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Homology is a general way of associating a sequence of algebraic objects such as abelian groups or modules to other mathematical objects such as topological spaces.

16 votes
1 answer
5k views

Is it true that all real projective space $RP^n$ can not be smoothly embedded in $R^{n+1}$ f...

$RP^3$ can not be embedded proving by homology thoery (Alexander sphere duality, lefschetz duality and a long exact sequence). For the other cases, I do not know how to prove. …
Xiaolei Wu's user avatar
  • 1,598
9 votes

Why torsion is important in (co)homology ?

Integer Pontrjagin classes are diffeomorphism invariant, while rational Pontrjagin classes are homeomorphism invariant, due to Novikov. Also there are examples where two smooth manifolds are homeomor …