Whitehead problem

In group theory, a branch of abstract algebra, the Whitehead problem is the following question:

Is every abelian group A with Ext1(A, Z) = 0 a free abelian group?

Not to be confused with Whitehead theorem or Whitehead conjecture.

Saharon Shelah proved that Whitehead's problem is independent of ZFC, the standard axioms of set theory.

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