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(Non) - Existence of complex structures on S⁶
In 1947, Heinz Hopf showed that there are infinitely many orientable even dimensional manifolds which admit no complex structure, including S⁴ and S⁸. He posed the question whether the same is true for S⁶. This problem, now known as the Hopf problem for S⁶, remains unsolved to this day. This working group summarized the state of research on this complex topic and eventually resulted in a special issue of the journal Differential Geometry and its Applications. Printed copies of this special volume are still available. Please contact Ilka Agricola if you would like to receive a copy.