@article{GDZPPN002076977, title = {Angles of a Parallelogram with Vertices in Lattice Points.}, journal = {Elemente der Mathematik}, volume = {24}, year = {1969}, pages = {114-115}, zbl = {0182.37801}, url = {http://dml.mathdoc.fr/item/GDZPPN002076977} }
Makowski, Andrzej. Angles of a Parallelogram with Vertices in Lattice Points.. Elemente der Mathematik, Tome 24 (1969) pp. 114-115. http://gdmltest.u-ga.fr/item/GDZPPN002076977/