Supposing we are given a signal x(t)
1) x(t) is real and odd
2) x(t) is periodic with period T = 2 and has Fourier coefficients $ ak $
3) $ ak = 0 $ for |k| > 1
4) $ \frac{1}{2} \int_{0}^{2} |x(t)|^2 dt = 1 $
