Abstract
We give the first examples of a pair of knots $K_1$, $K_2$ in the 3-sphere for which their unknotting numbers satisfy $u(K_1\#K_2)< u(K_1) +u(K_2)$. This answers question 1.69(B) from Kirby’s problem list, in the negative.
We give the first examples of a pair of knots $K_1$, $K_2$ in the 3-sphere for which their unknotting numbers satisfy $u(K_1\#K_2)< u(K_1) +u(K_2)$. This answers question 1.69(B) from Kirby’s problem list, in the negative.
