  Comparison of solar-neutrino signals in SNO and Super-Kamiokande (SK)
detectors results in discovery of $\nu_e \to \nu_{\mu,\tau}$ oscillations at
level $3.1 - 3.3 \sigma$ \cite{SNO}. This comparison involves the assumption of
neutrino spectrum and a choice for the thresholds of detection in both
experiments. In this Letter we obtain an exact formula for the comparison of
the signals which is valid for arbitrary spectra and thresholds. We find that
the no-oscillation hypothesis is excluded at 3.3$\sigma$. If the
energy-dependent component of the survival probability for electron neutrinos
is small as compared with the average value, i.e. in the case of small
distortion of the observed spectrum, the oscillation hypothesis can also be
tested to similar accuracy. The oscillation to sterile neutrino only, is
excluded at $3.3 \sigma$ level, and oscillation to active neutrinos is
confirmed at the same level, though with some reservations.
