  The unknotting number of a knot is bounded from below by its slice genus. It
is a well-known fact that the genera and unknotting numbers of torus knots
coincide. In this note we characterize quasipositive knots for which the genus
bound is sharp: the slice genus of a quasipositive knot equals its unknotting
number, if and only if the given knot appears in an unknotting sequence of a
torus knot.
