Try Masyu
Here is a Masyu puzzle that you can solve in your browser. Remember that the goal of Masyu is to draw a single nonintersecting loop through all of the circles in the grid. Click and drag to add and remove edges. The puzzle has exactly one solution. When you've found it, the puzzle background will turn green. To reset the puzzle, just reload this page.
Black Circles
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The path must turn at each black circle and go straight for two line segments forward and back.
White Circles
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The path must go straight through each white circle and turn on at least one segment immediately before or after the white circle.
One Loop
The path must form a single loop.