On Difference-Sets

The positive integers d₁.. ,d_t incongruent (mod m) are said to form a difference-set (mod m ; m₁,...,m_r), where m₁,..., m_r are any factors of m, if the number of solutions of the congruence g congruent to d_i-d_j (mod m) (i,j taking values from I to t both inclusive), is independent of g, whenever g is not a multiple of m₁..., m_r. We call the set as a difference-set of t integers (mod m; m₁,...,m_r).