Appendix 1.
Photos of impossible figures.

Jerry Andrus from USA have been enthusiastic about contructioning impossible figures. The left photo shows crazy crate created by him, and the right photo shows us the same figure from other point of view.

There's another two photos with Jerry Andrus against a background of his impossible screw.

Below, you can see another example of impossible figure created by american photographer and artist Walter Wick. The figure resemples in appearance the crazy crate. The construction of the figure differs from Andrus's crate.

Impossible figures by Elber Gershon.

Elber Gershon works at Technion institute in Israel and engaged in modelling impossible figures on computer. Some modelled figures were printed on 3D-printers Zcorporation and Stratasys. Below you can see some figures created by Elbel Gershon. All models you can find here http://www.cs.technion.ac.il/~gershon/