Yin-Yang
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Yin-Yang is a logic puzzle with simple rules and challenging solutions.
The rules are simple.
Yin-Yang is played on a rectangular grid with no standard size. Some cells start out filled with black or white. The rest of the cells are empty.
The goal is to color all cells in such a way that:
1. All black cells should be connected orthogonally in a single group.
2. All white cells should be connected orthogonally in a single group.
3. 2x2 areas of the same color are not allowed.
These 3 simple rules lead to some complex deductions, which are not so obvious. There are 2 important lemmas based on them, without which even the easy Yin-Yang puzzles seem very hard or even impossible to approach.
You can learn these lemmas in the video tutorial below.