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Sudoku is not for the weak. 

A hand model on the cover of sudoku book Sudoku Challenger proves that the puzzles therein are extremely difficult. So much so that the person on the cover can't get one right.

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Reddit user wherearemyflapjacks posted a photo of the book to the site and people are flabbergasted by the faux pas. 

CARD ID: 35181, CARD TYPE: Imgur

For those of you who aren't sudoku-literate, the nine small squares that make up one large square must be filled with numbers 1-9, without repeats. 

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Unfortunately for the hand on the cover, the number five has already been used in that group of nine squares.

We'd call the cover model dumb, but at least they were smart enough to use a pencil instead of a pen.

In case this mistake isn't enough for you to put this book back on the shelf, Reddit commenters pointed out another blunder in addition to five-gate.

Comment from discussion Sudoku book cover is of someone making a mistake.

So is it sudoku, or sudok-hue?

The world may never know.

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(责任编辑：探索)