Hi iMaterialise fans,
Oskar Key was originally designed in 1987, based on an idea from 1984. This two-layer puzzle key was mass-produced in metal by the Japanese Hanayama toy company. It was the very first licensed design by Hanayama. Production has stopped a long time ago, and vintage samples are occasionally sold at Ebay for 1000 USD. Several people asked me for a 3D-printable sample, so here it is. To make the puzzle even more challenging, I added a third key in the middle. The underlying mathematical concept is Prof. N.G. de Bruijn’s Beer Bottle Problem (see https://vixra.org/pdf/1208.0223v1.pdf, page 110), who proved in the 1960’s (?) that such puzzle is always solvable.