Tango: the sun and moon puzzle game

Tango is a binary logic puzzle, from the same family as takuzu and binairo: every cell holds one of two symbols, and a few counting rules decide which one. In Tango the symbols are a sun and a moon, and small = and × markers between cells add extra clues.

There is no arithmetic and no luck. Each board starts with some symbols in place, and every empty cell can be worked out from the rules and the markers.

• Each row and each column holds three suns and three moons.
• No more than two of the same symbol may sit next to each other in a row or column.
• Cells joined by = hold the same symbol.
• Cells joined by × hold opposite symbols.

Every board is checked when it is generated to have exactly one solution, so careful reasoning always gets you to the end.

Tango generates its boards on your phone, so you never run out. Difficulty climbs through four tiers, from easy to expert: early boards give you plenty of symbols to start from, and later ones give you far fewer, leaning on the = and × markers instead.

Undo is free and unlimited, so you can test an idea and take it back. When you are stuck, Hint fills in one cell that the rules force, which usually unlocks the next few moves. A long press clears a cell, and Reset starts the board over.

Solved boards earn points on the This Week leaderboard, with harder boards worth more, and the All Time board ranks players by the highest level reached.