On the separability of quadrilaterals in the plane by translations and rotations (Q2400117)

The object of the paper is, as stated in the abstract, as follows: ``A proof is given that for all positive integers \(n\geq 7\) there exist sets of \(n\) non-overlapping quadrilaterals in the plane, such that no non-empty proper subset of these quadrilaterals can be separated from its complement, as one rigid object, by a single translation, without disturbing its complement. Furthermore, examples are given for which no single quadrilateral can be separated from the others by means of translations or rotations.'' The problem, as treated in the paper, turned out to be tricky to solve. The authors handle it by elementary methods, such as connections between arcs and by means of trigonometry. As such, the paper is readable and understandable for any person educated in college years and lower university years. But there is more in this paper, not covered in the research about the problem. It contains an illuminating introduction on two- and three-dimensional dissecting and rotational and translation questions in the near past. Commutations with robotics is densely explained. Therefore, the paper is very instructive for students as well as for specialists, even for those people working in industry and mechanical production.