1. Escher M.C. 〈http://www.mcescher.com〉.
2. Elber G. The “escher for real” project. 〈http://www.cs.technion.ac.il/∼gershon/EscherForReal〉.
3. Lipson A. Andrew lipson's lego page project. 〈http://www.andrewlipson.com/lego.htm〉.
4. Computer-aided creation of impossible objects and impossible motions;Sugihara,2007
5. Putting order in the impossible;Kupla;Peceptions,1987