  We consider how superfluidity of dripped neutrons in the crust of a neutron
star affects the frequencies of the crust's fundamental torsional oscillations.
A nonnegligible superfluid part of dripped neutrons, which do not comove with
nuclei, act to reduce the enthalpy density and thus enhance the oscillation
frequencies. By assuming that the quasi-periodic oscillations observed in giant
flares of soft gamma repeaters arise from the fundamental torsional
oscillations and that the mass and radius of the neutron star is in the range
of 1.4 < M/M_SUN < 1.8 and 10 km < R < 14 km, we constrain the density
derivative of the symmetry energy as 100 MeV < L < 130 MeV, which is far
severer than the previous one, L > 50 MeV, derived by ignoring the
superfluidity.
