A hexagonal crystal hides dislocations. Walk Burgers circuits around regions you choose, read how far each circuit misses closing, and flag every defect with its Burgers vector.
The crystal. Each hexagon is one atom site of a triangular lattice with lattice vectors a₁ (east) and a₂ (60° up). Some sites hold the core of an edge dislocation, whose Burgers vector is one of the six nearest-neighbor steps.
A Burgers circuit. Pick any region and walk around its boundary, counting lattice steps as if the crystal were perfect. In a perfect crystal you return to the start. Around dislocations you miss by the sum of the enclosed Burgers vectors. This is Stokes' theorem for a lattice: the closure failure is the total dislocation content inside.
Cancellation. Two defects with opposite Burgers vectors cancel, so a circuit that closes does not prove its region is empty. On the Hard level the whole crystal sums to zero, just as a bent crystal's dislocations must when they come in pairs.
Scoring. Every circuit costs 1. The free boundary circuit is already in the log. A wrong check adds 2 and tells you how many cells are wrong, but not which. Lower is better; par is a rough binary-search budget.
Controls. In Select region, click or drag to paint cells. In Place flags, click a cell to cycle its flag through the six directions and back to empty. Keys: F switches mode, Enter walks the circuit, Esc clears the selection.
After the game. Crystal view draws the atoms displaced by the Volterra field u = Σ bᵢ θᵢ/2π. Bonds join atoms that end up about one spacing apart, so each core shows up as a snag in the net where an extra half-row of atoms ends.