# A Sneaky Yin-Yang Puzzle

Here is a standard Yin-Yang puzzle.

Rules of Yin-Yang:

1. Fill each empty cell with either a black circle or a white circle.
2. All white circles should be orthogonally connected, so do all black circles.
3. There may not be any 2x2 cell region consisting of the same circle color.

I couldn't find a suitable starting logic without a not-well-known trick:

In a puzzle with even width and height, the border cells excluding the corners are divided into dominoes, each of which is to be colored in a single color. So the bottom left corner starts as this:

Apply some easy deduction and use the "border pair" logic once more:

Some more easy deduction, and we realize that the white must go all around the board by border connectivity logic. Sneaky!

Then the chain of easy deduction finishes the puzzle:

• "Fill each empty cell with either a black circle or a white circle." ;-) Nov 29, 2020 at 15:14
• @Florian I believe that has been left as an exercise for the reader. Nov 29, 2020 at 15:59
• Correct and well done! :D (The technique is apparently mentioned way back then here in PSE: A problem about Yin-Yang puzzles) Nov 30, 2020 at 0:57
• @athin Yeah, I learned it through that exact post :) Nov 30, 2020 at 1:00