# Relative difference set for a subgroup

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