Scharlemann, Martin Heegaard reducing spheres for the 3-sphere. (English) Zbl 1030.57031 Rend. Ist. Mat. Univ. Trieste 32, Suppl. 1, 397-410 (2001). In a previous paper with W. Thurston the author defined an invariant in \({\mathbb Q}/2\) of a knot with unknotting tunnel \(\gamma\). To construct this invariant they characterized reducing spheres for genus two Heegaard splittings of \(S^3\). In the paper under review the author generalizes this characterisation to arbitrary genus Heegaard splittings of \(S^3\) and proves that there always exists a sequence of complete collections of reducing spheres with some conditions. Reviewer: Vincent Blanloeil (Strasbourg) Cited in 2 Documents MSC: 57N12 Topology of the Euclidean \(3\)-space and the \(3\)-sphere (MSC2010) 57N10 Topology of general \(3\)-manifolds (MSC2010) Keywords:Heegaard spliting; reducing sphere; 3-sphere × Cite Format Result Cite Review PDF