Bílka, O., K. Buchin, R. Fulek, M. Kiyomi, Y. Okamoto, S.- ichi Tanigawa, and C. D. Tóth. “A Tight Lower Bound for Convexly Independent Subsets of the Minkowski Sums of Planar Point Sets”. The Electronic Journal of Combinatorics, Vol. 17, no. 1, Oct. 2010, p. N35, doi:10.37236/484.