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First of all, what I want to ask is slightly more elaborate than what stands in the title (hence the subquestion). I am telling this since as it is, the title contains a meaningful question, but it ...

I am a physics student, recently I read a paper using Homotopy $\pi_4(SU(2))=Z_2$, I guess mathematicians have some visualization or explanation of this result. So I come here ask for help. CROSS-...