On the Subject of Mahjong

Plum, Orchid, Chrysanthemum, Bamboo. Remember that.

• Take the first character of the serial number. If it’s a letter, take its alphabetic position and add 9. If this is not in the range 0–13, subtract 14 until it is.
• Find the Mahjong tile in that position in the first Match Row below, counting from 0.
• Perform the same calculation with the second character of the serial number and find the corresponding Mahjong tile in the second Match Row.
• Swap those two tiles.
• Do the same again with the third and fourth character, then once more with the fifth and sixth.

Match Rows

0 5 10

← →

• Identify the extra tile in the bottom-left corner of the module and determine its position in the Counting Row below, counting from 0.
• Cycle the bottom Match Row to the right by that many tiles.

Counting Row

0 5 10

• On the module, a tile is “available” if either its left or its right edge has no tile adjacent to it, and no tile is (even partially) on top of it.
• Select pairs of available tiles on the module whose likenesses are vertically aligned in the modified Match Rows.
• A correct pair disappears. An incorrect pair incurs a strike.
• Once all tiles are eliminated, the module is disarmed.