SENOUSSI, Bendehiba, and Mohammed BEKKAR. “Helicoidal Surfaces With Δ ᴶ ᵣ = Ar in 3-Dimensional Euclidean Space”. Studia Universitatis Babeș-Bolyai Mathematica, vol. 60, no. 3, Sept. 2015, pp. 437-48, https://studia.reviste.ubbcluj.ro/index.php/subbmathematica/article/view/5796.