Proving Hopf Invariant and Degree of g for f⋅g

[eok20]

Can someone give me some hints on how to prove the following statement: if f: S^3 \to S^2, g: S^3 \to S^3 then H(f\circ g) = deg~g H(f) where H is the Hopf invariant and deg g is the degree of g. I'm pretty clueless on how to start and I don't see how to get the deg to come in since that has to do with 3-d cohomology but the Hopf invariant has to do with 2-d and 4-d cohomology.

Thanks.

 

[quasar987]

I don't know what definitions you are using, but with the definition of the Hopf invariant given at page 227-228 of Bott-Tu and then using the caracterisation of degree found at http://en.wikipedia.org/wiki/Degree_of_a_continuous_mapping#Differential_topology, it is very simple.

 

[eok20]

I don't know what definitions you are using, but with the definition of the Hopf invariant given at page 227-228 of Bott-Tu and then using the caracterisation of degree found at http://en.wikipedia.org/wiki/Degree_of_a_continuous_mapping#Differential_topology, it is very simple.

Thanks-- I should have clarified. I'm interested in the algebraic topological definition and proof. Here, the Hopf invariant is the integer h such that \alpha \smile \alpha = h\beta where \alpha generates the 2-d cohomology and \beta generates the 4-d cohomology of the mapping cone of f:S^3 \to S^2. The degree of g:S^3\to S^3 is the integer d such that f_* \gamma = d\gamma where \gamma generates the 3-d homology of S^3.

Unfortunately, I have very little intuition/feel for algebraic topology and I much prefer the differential forms and differential topology analogs.