1. Each row and each column must contain the numbers 1 through 4 (easy) or 1 through 6 (challenging) without repeating.
2. The numbers within the heavily outlined boxes, called cages, must total the target number in the top left of the cage, using the math operation given. For example 2- means the numbers in the cage total 2 through subtraction (3 and 1 or 4 and 2, in any order).
3. Freebies: In single-box cages, fill in the number in the top-left corner of that cage. A good way to start is to fill in these boxes first.