for r being Real
for i being Integer st PI + ((2 * PI) * i) <= r & r <= ((3 * PI) / 2) + ((2 * PI) * i) & r / PI is rational & sin r is rational holds
r in {(PI + ((2 * PI) * i)),(((7 * PI) / 6) + ((2 * PI) * i)),(((3 * PI) / 2) + ((2 * PI) * i))}