General

• Rewrite exact_cover.py in C as an extension module.
• Complete unit tests.
• Implement a graphical front-end. Ideas:
  • The ability to turn pieces on or off, and control the number of instances of each piece.
• Restore state from a solution file instead of from a saved state file? I.e. use the last solution in the solution file to simulate a saved state file.

Puzzles

To implement:

• pentominoes:
  • ring/tube versions of 3x20, 4x15, 5x12, 6x10 (joined at short or long edges)
  • toroidal versions of 3x20, 4x15, 5x12, 6x10
  • Möbius strip versions of 3x20, 4x15, 5x12, 6x10 (joined at short or long edges)
  • Klein bottle?
• polyiamonds:
  • O'Beirne's hexagon one-sided hexiamond problem? (see Knuth's "Dancing Links" paper)
• polyhexes
  • Order 1 through 5 (like Kadon's Hexnut)?
  • Hexahexes (e.g. Kadon's Hexnut II)?
• 15/16 tetrasticks: aztec diamond of order 3; unbordered 7x7 grid; 3x5 diamond lattice
• polysticks of order 1-4: unbordered 8x8 grid