geometry-topology / 4-manifold topology

The Kinoshita Conjecture and Kirby Problem 4.37

Kinoshita conjectured that every embedded projective plane in $S^4$ is reducible. False: an irreducible embedded projective plane exists in $S^4$. The construction also answers both parts of Problem 4.37 of the Kirby problem list.

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geometry-topologyMay 13, 2026Significance 35/100Registry: unreviewed

The Kinoshita Conjecture and Kirby Problem 4.37

Prior state unknowndisproved

Kinoshita conjectured that every embedded projective plane in $S^4$ is reducible. False: an irreducible embedded projective plane exists in $S^4$. The construction also answers both parts of Problem 4.37 of the Kirby problem list.

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Kinoshita conjectured that every embedded projective plane in $S^4$ is reducible. False: an irreducible embedded projective plane exists in $S^4$. The construction also answers both parts of Problem 4.37 of the Kirby problem list.

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