EN
We describe all sets $A ⊆ 𝔽_p$ which represent the quadratic residues $R ⊆ 𝔽_p$ in the sense that R = A + A or R = A ⨣ A. Also, we consider the case of an approximate equality R ≈ A + A and R ≈ A ⨣ A and prove that A is then close to a perfect difference set.