Step 2 of 6
No tree, no tent
Every tent needs a tree beside it. The clearings without one are grass, all of them, right now.
The rule of thumb: A tent must stand beside a tree. A clearing with no tree next to it can never hold a tent — grass it.
A tent must stand beside its tree — up, down, left or right, never diagonal. A clearing with no tree on any of its four sides can never hold a tent, whatever the counts say. Make the sweep your first real move: walk the board once and grass every one of them.
It’s the cheapest information in the game, and the worked example below shows the size of it: a single pass rules out a big share of the board before anything is counted. These practice boards lean on the sweep — skip it and the counts never narrow enough to force the tents.
Where to look: Clearings out in the open, away from the trees. Check all four sides; a tree on the diagonal doesn’t count.
Worked example
A real position from a board that needs No tree, no tent. Purple: what the reasoning rests on. Dashed: the cells in question. Green: what it proves.
The sweep is a habit now. Next: what a pitched tent forbids around itself. Step 3: Tents need elbow room →