  We reformulate the probabilities of disappearance neutrino or antineutrino
oscillations so as to single out the interference term proportional to the
product of \sin[\Delta m^2_{21} L/(4 E)] and \sin[(\Delta m^2_{31} + \Delta
m^2_{32}) L/(4 E)], which is transparently sensitive to the neutrino mass
ordering. We elaborate this issue for a reactor-based antineutrino oscillation
experiment like JUNO, and take account of terrestrial matter effects. If a
light sterile neutrino species contributes to P(\overline{\nu}_e \to
\overline{\nu}_e), we find that there will be a new interference term
proportional to the product of \sin^2 2\theta_{14}, \sin[\Delta m^2_{21} L/(4
E)] and \sin[(\Delta m^2_{41} + \Delta m^2_{42}) L/ (4 E)] in the standard
parametrization of the (3+1) X (3+1) active-sterile neutrino mixing matrix.
