Relative difference set for a subgroup

Definition
A subset $$D$$ of a group $$G$$ is termed a relative difference set with forbidden subgroup $$N$$ if:


 * No non-identity element of $$N$$ can be expressed as a right quotient of elements of $$D$$
 * Every element outside $$N$$ can be expressed as a right quotient of elements of $$D$$ in exactly $$\lambda$$ ways where $$\lambda$$ is a constant independent of the choice of element

Related notions

 * Difference set
 * Divisible difference set for a subgroup