Ruscheweyh, Stephan, and C. Luis Salinas. “On the Preservation of Direction-Convexity and the Goodman-Saff Conjecture”. Annales Fennici Mathematici 14, no. 1 (February 1, 1989): 63–73. Accessed November 25, 2024. https://afm.journal.fi/article/view/134647.