Appearance-Disappearance Relation in 3+$N_{s}$ Short-Baseline Neutrino
  Oscillations
  We derive the relation between the amplitudes of short-baseline appearance
and disappearance oscillations in 3+$N_{s}$ neutrino mixing schemes which is
the origin of the appearance-disappearance tension that is found from the
analysis of the existing data in any 3+$N_{s}$ neutrino mixing scheme. We
illustrate the power of the relation to reveal the appearance-disappearance
tension in the cases of 3+1 and 3+2 mixing using the results of global fits of
short-baseline neutrino oscillation data.
