The classic '9-dot puzzle' demonstrates that connecting a 3x3 grid of dots with straight, continuous, non-retracing lines requires thinking 'outside the box' -- literally extending lines beyond the boundary of the dot grid -- and the minimum solution uses 4 straight lines.
The 9 dots arranged in a 3x3 grid can be connected without lifting the pen and without retracing any path using a minimum of 4...
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