-fold interleaving of a periodic binary sequence of length
with out-of-phase (normalized) autocorrelation
. Examples of binary sequences with such out-of-phase autocorrelation (termed two-level sequences) are: 1) maximal-length linear shift-register footnote[1]{sequences}, 2) twin-prime footnote[2]{sequences}, 3) quadratic residue footnote[3]{sequences}, and 4) Hall foonote[4]{sequences}.