The levels were taken (with permission) from:
www: http://xsokoban.lcs.mit.edu/xsokoban.html
author: Andrew Myers <andru@lcs.mit.edu>
www: http://www.lysator.liu.se/˜ingemar/games.html
author: Ingemar Ragnemalm <ingemar@lysator.liu.se>
www: http://members.aol.com/SokobanMac/
author: Scott Lindhurst <scottl@alumni.Princeton.EDU>
www: http://www.ne.jp/asahi/ai/yoshio/sokoban/main.htm
author: Yoshio Murase <yoshio@asahi.email.ne.jp>