geometry-topology / Topological 4-manifolds; surgery and disc embedding

The four-dimensional disc embedding conjecture and whether the free group is good

Theorem 1.1: there is a compact oriented smooth 4-manifold MM with immersed proper discs f1,…,fkf_1,\dots,f_k with embedded boundary circles and framed (even smoothly embedded) spheres gig_i satisfying λ(fi,gj)=δij\lambda(f_i,g_j)=\delta_{ij}, λ(gi,gj)=0\lambda(g_i,g_j)=0, μ~(gi)=0\widetilde\mu(g_i)=0, whose boundary circles bound no pairwise disjoint locally flat discs, in any relative homotopy class. Corollary 1.2: F2F_2, and every group containing it, is not good in the Freedman-Quinn sense. Corollary 1.3: the unrestricted topological surgery and s-cobordism assertions cannot both hold. The marked tensor companion proves the framing-preserving version. Not shown: which of surgery or s-cobordism fails, or that the Borromean rings are not A-B slice.

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geometry-topologySep 24, 2026Significance 60/100Registry: unreviewed

The four-dimensional disc embedding conjecture and whether the free group is good

Prior state unknown→disproved

Theorem 1.1: there is a compact oriented smooth 4-manifold MM with immersed proper discs f1,…,fkf_1,\dots,f_k with embedded boundary circles and framed (even smoothly embedded) spheres gig_i satisfying λ(fi,gj)=δij\lambda(f_i,g_j)=\delta_{ij}, λ(gi,gj)=0\lambda(g_i,g_j)=0, μ~(gi)=0\widetilde\mu(g_i)=0, whose boundary circles bound no pairwise disjoint locally flat discs, in any relative homotopy class. Corollary 1.2: F2F_2, and every group con…

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Theorem 1.1: there is a compact oriented smooth 4-manifold MM with immersed proper discs f1,…,fkf_1,\dots,f_k with embedded boundary circles and framed (even smoothly embedded) spheres gig_i satisfying λ(fi,gj)=δij\lambda(f_i,g_j)=\delta_{ij}, λ(gi,gj)=0\lambda(g_i,g_j)=0, μ~(gi)=0\widetilde\mu(g_i)=0, whose boundary circles bound no pairwise disjoint locally flat discs, in any relative homotopy class. Corollary 1.2: F2F_2, and every group containing it, is not good in the Freedman-Quinn sense. Corollary 1.3: the unrestricted topological surgery and s-cobordism assertions cannot both hold. The marked tensor companion proves the framing-preserving version. Not shown: which of surgery or s-cobordism fails, or that the Borromean rings are not A-B slice.

Theorem 1.1: there is a compact oriented smooth 4-manifold MM with immersed proper discs f1,…,fkf_1,\dots,f_k with embedded boundary circles and framed (even smoothly embedded) spheres gig_i satisfying λ(fi,gj)=δij\lambda(f_i,g_j)=\delta_{ij}, λ(gi,gj)=0\lambda(g_i,g_j)=0, μ~(gi)=0\widetilde\mu(g_i)=0, whose boundary circles bound no pairwise disjoint locally flat discs, in any relative homotopy class. Corollary 1.2: F2F_2, and every group containing it, is not good in the Freedman-Quinn sense. Corollary 1.3: the unrestricted topological surgery and s-cobordism assertions cannot both hold. The marked tensor companion proves the framing-preserving version. Not shown: which of surgery or s-cobordism fails, or that the Borromean rings are not A-B slice.

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The four-dimensional disc embedding conjecture and whether the free group is good — Mathematical Frontier Network