Following an example discovered by John Berge, we show that there is a
4-component link L \subset (S^1 x S^2)#(S^1 x S^2) so that, generically, the
result of Dehn surgery on L is a 3-manifold with two inequivalent genus 2
Heegaard splittings, and each of these Heegaard splittings is of Hempel
distance 3.
A gap in a paper of Rubinstein-Scharlemann is explored: new examples are
found of closed orientable 3-manifolds with possibly multiple genus 2 Heegaard
splittings. Properties common to all the examples in the original paper are not
universally shared by the new examples: some of the new examples have Hempel
distance 3, and it is not clear that a single stabilization always makes the
multiple splittings isotopic.
A gap in a paper of Rubinstein-Scharlemann is explored: new examples are
found of closed orientable 3-manifolds with possibly multiple genus 2 Heegaard
splittings. Properties common to all the examples in the original paper are not
universally shared by the new examples: some of the new examples have Hempel
distance 3, and it is not clear that a single stabilization always makes the
multiple splittings isotopic.
A knot K in the 3-sphere is said to have Property nR if, whenever K is a
component of an n-component link L and some integral surgery on L produces the
connected sum of n copies of S^1 x S^2, there is a sequence of handle slides on
L that converts L into a 0-framed unlink. The Generalized Property R Conjecture
is that all knots have Property nR for all n.