Jeff Heldt

Brain Tickler: Mathrax Puzzles - The Best Japanese Puzzles Collection - Logic Puzzle Books Jeff Heldt

Mathrax consists of a square grid. The goal is to fill in each cell with numbers from 1 to N, where N is the size of the puzzle's side. No number may appear twice in any row or column. Circles with additional conditions may be situated on intersections of lines inside the grid; a circle may contain:
- A number and a sign of mathematical operation (addition, subtraction, multiplication, division) - a number is a result of an operation execution with numbers in diagonally adjacent cells.
- A letter "E" ("even") - all numbers in four cells are even.
- A letter "O" ("odd") - all numbers in four cells are odd.

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