theorem :: NIVEN:65

for r being Real
for i being Integer st (PI / 2) + ((2 * PI) * i) <= r & r <= PI + ((2 * PI) * i) & r / PI is rational & sin r is rational holds
r in {((PI / 2) + ((2 * PI) * i)),(((5 * PI) / 6) + ((2 * PI) * i)),(PI + ((2 * PI) * i))}