How to play

Lattice Five is Morpion Solitaire (Join Five) — a solitaire played on grid paper since the 1970s. The rules fit in a paragraph; mastering them doesn’t.

The rules

1. Play starts from a cross-shaped pattern of 36 dots.
2. On each move, place one new dot anywhere on the grid, then draw a straight line through five consecutive dots — horizontal, vertical, or diagonal. The line must include the dot you just placed.
3. No segment may be drawn twice. In the classic 5T rules, two lines in the same direction may share an endpoint dot, but never overlap; in the stricter 5D variant they may not even touch.
4. When no legal move remains, the game is over. Your score is the number of lines you drew.

That’s all of it. The depth comes from one subtlety: a line can only be drawn on the move that creates it — five dots already in a row are worth nothing. Every placement is a trade between scoring now and keeping the position alive.

How good is good?

On the classic cross under 5T rules, beginners typically reach the 40s–60s. The human record of 170 was set by hand in 1976 and stood for 34 years; the best computer-found game is 178. Nobody knows the true maximum — only that it’s at most 485.

In the app

• Tap an empty point to see every line it could make; tap a line to play it. Drag over the candidates and lift to choose. Hover works too, with a mouse or trackpad.
• Free play offers unlimited undo and all the variants; the daily is one attempt at the day’s shared board, one undo per move.
• The chart under the board shows your position’s openness — legal moves available — against your best game’s curve. Stay above the ghost.