Whitehead problem
the problem of whether an abelian group 𝐴 satisfying Ext¹(𝐴,ℤ)=0 is necessarily free, now known to be independent of ZFC
en-GB/ˈwaɪthɛd ˈpɹɒbləm/
en-US/ˈwaɪtˌhɛd ˈpɹɑbləm/
the problem of whether an abelian group 𝐴 satisfying Ext¹(𝐴,ℤ)=0 is necessarily free, now known to be independent of ZFC