Irreducible components of canonical graphs for second order spectral nulls

Irreducible components of canonical graphs for second order spectral null constraints at a frequency f=f_sk/n, where f_s is the symbol frequency, and k and n, integers with k⩾0 and n>0. We show that if n is prime then a canonical graph consists of disjoint irreducible components. We also show that the number of irreducible components of a canonical graphs is finite. For the case n=2, all aperiodic irreducible components are identified