Pro Tip

Before using pencil marks, see how far you can get on a hard puzzle with pure mental tracking.

Pro Tip
✓ Completed! 👍
6
2
9
7
6
5
7
3
8
5
2
4
1
3
9
1
4
8
6
9
8
2
2
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7
4
Scientific Mind

"A theory that is not refutable by any conceivable event is non-scientific." — Karl Popper

Scientific Mind