  Given knots K and J, one can ask whether a single smoothing of a crossing in
a diagram for K can convert it into a diagram for J. As an interesting example,
Zekovic discovered that the torus knot T(2,5) can be converted into T(2,-5)
with a single smoothing. On the other hand, Moore and Vasquez have shown that
among torus knots of the form T(2,m), T(2,5) is the only one which can be
converted into its mirror image with a single smoothing, assuming that m is
square free. In this paper, Casson-Gordon theory is applied to extend the
Moore-Vasquez result to all torus knots T(2,m), with the exception of T(2,9),
which remains an open case. Applications of similar techniques to the general
problem are also described, as are tools arising from Heegaard Floer theory.
