- ➊ Write numbers from 1 to N into the cells of the diagram of size NxN, so that each number occurs exactly once in each row and each column.
- ➋ Some intersections of the grid lines are marked by a number and an operator (+, –, *, ÷) in a circle.
- ➌ The number is the result of the operation, applied to both pairs of diagonally opposite cells.
- ➍ An "e" in the circle indicates that all four adjacent numbers are even; an "o" indicates that all four adjacent numbers are odd.