Helmut Alt Hans L. Bodlaender Marc J. van Kreveld Günter Rote Gerard Tel Wooden Geometric Puzzles: Design and Hardness Proofs. 16-29 2007 conf/fun/2007 FUN http://dx.doi.org/10.1007/978-3-540-72914-3_4 db/conf/fun/fun2007.html#AltBKRT07