This is a Toroidal Heyacrazy puzzle.
Rules of Heyacrazy:
Shade some cells of the grid.
Shaded cells cannot be orthogonally adjacent; unshaded cells must be orthogonally connected.
When the puzzle is solved, you must not be able to draw a line segment that passes through two borders, and does not pass through any shaded cells or grid vertices.
For an example puzzle and its solution, see this question.
Additional rule for Toroidal Heyacrazy:
- The grid 'wraps around' on both sides, with the right side connecting to the left side and the top connecting to the bottom. Red lines mark where the grid wraps around, but otherwise have no effect. (In particular, they do not count as 'borders' for the previous rule). Nine copies of the grid have been provided for your convenience.
The vanilla puzzles are done, now on to the variants! This is the first of three variant puzzles I've made - I noticed that in standard Heyacrazy puzzles, you can often figure out that the corner is unshaded simply because there are no adjacent walls, and so nothing can force it to be shaded. This is a puzzle that doesn't suffer from that particular problem.