The Dirac comb is quoted as the only self-Fourier-Fresnel function. Ot
her dual self-transform functions (DSTFs) known to us are approximate.
We show that for arbitrary transformable even periodic function p(x,y
), the functions f(x,y) = p(x,y)comb(x,y) + p(Fo)(x,y) comb(x, y) ar
e DSTFs.