Sl. Ma et B. Schmidt, Relative (p(a), p(b), p(a), p(a-b))-difference sets: A unified exponent bound and a local ring construction, FINITE F T, 6(1), 2000, pp. 1-22
We show that for an odd prime p the exponent of an abelian group of order p
(a+b) containing a relative (p(a), p(b), p(a), p(a-b))-difference set canno
t exceed p([a/2] + 1). Furthermore, we give a new local ring construction o
f relative (q(2u), q, q(2u), q(2u-1))-difference sets for prime powers q. F
inally, we discuss an important open case concerning the existence of abeli
an relative (p(a), p, p(a), p(a-1))-difference sets. (C) 2000 Academic Pres
s.