# Mathrax

## Rules edit

Enter numbers from 1 to X into the grid, so that each number appears exactly once in each row and column. Some grid points contain a clue consisting of a number and an arithmetic operator. The clue number must be the result of the given operator being applied to a pair of diagonally opposite adjacent cells, and it must be valid for both such pairs of cells. If a grid point is marked with an E (“even”) or O (“odd”), then all four adjacent cells must contain even respectively odd numbers.

(Rules (modified) and example from WPC 2019 IB)

## History of the puzzle edit

Invented by Otto Janko (Austria) in 2010. ^{[1]}

## Appearances in the past WPCs edit

- WPC 2019/Round 7 by Ulrich Voigt
- WPC 2018/Round 9 by František Luskač
- WPC 2018/Individual Playoffs by František Luskač
- WPC 2017/Round 16 by Rajesh Kumar
- WPC 2014/Round 4