Object: create an identical covering on both boards.

In a double-decker puzzle you are given two type of tiles.
With each tile you are supposed to tile an area that can also be tiled by the other of the two tiles.

Hence you play on two boards at the same time, until the areas covered on each board are the same.

Click one of the pairs in the menu to start the game.

Instructions for playing:
You win if you manage to tile the given area.

Click an empty position to create a new tile.
If the new tile overlaps with existing tiles or is partially placed out side the board, the system will ask you to rotate it or delete the tile.

Click a tile's handle (the little marker) to rotate this tile.
With each click the tile will be rotated anticlockwise by 90 degrees.
Tiles that are not symmetrical will turn into their mirror image after four clicks, and after eight clicks will revert to the original unmirrored version.

Click the DELETE button to delete the tile which was handled (i.e., created or rotated) last.
If you want to delete a tile other than the one handled last, rotate it first by clicking it.

Click the COMPARE button to display (in black) the differences in coverage.
The goal is to have no differences in covered area.
The COMPARE makes very obvious which positions are covered by only one of the two sets.
You can add and turn tiles while COMPARE is active.
Click the COMPARE button again to return to normal play.
At the start the COMPARE mode is active by default.

Please note that there is an alternative piece set available (with a thinner rim).

Double-Decker puzzles are also called 'polyomino compatibility problems'.
While several web site display solutions to this kind of problems, it seems that this Zillions game is the first computer program which lets you, the user, try to solve double-decker puzzles interactively.
Double-Decker puzzles have been more and more investigated over the last 10 years.
Some of these geometrical tiling problems are very difficult to solve, since the area to be tiled is unknown.
Some puzzlists (such as G.Resta in 2009) wrote computer programs to find solutions.

Related Zillions game: 'Double-Decker Puzzle'.

Links:
http://www.iread.it/Poly
http://userpages.monmouth.com/~colonel/n5com/n5com.html

For related puzzles see also:
http://www.iread.it/lz/triplep.html
http://www.iread.it/lz/oddpairs.html