The Langford (4, n)-sequence: A trigonometric approach. - Sadao Saito; Takanori Hayasaka (Discret. Math., 1979)

Langford sequences: Some connections with complete and additive permutations. - Sadao Saito; Takanori Hayasaka (Discret. Math., 1990)

Further results on irregular, critical perfect systems of difference sets II: systems without splits. - Takanori Hayasaka; Sadao Saito; Douglas G. Rogers (Discret. Math., 1992)