Sixteen relations between observables in nucleon-nucleon scattering

Assuming all the usual invariance properties (parity, time-reversal, identical particles) in $p-p$ elastic scattering, twenty-five independent observables are available if one can detect the spin of each particle in all possible configurations. Since the scattering matrix depends upon nine real functions of $s$ and $t$, up to an over-all phase, one expects sixteen independent relations between the observables. To derive these relations, we give a simple method which is valid for any scattering process.