Normal Sudoku rules apply: enter the digits 1 to 9 in each column, row, and 3×3 box.

The circle is an odd digit. The square is an even digit.

The less-than signs point at the smaller value between two cells.

The skyscraper clues show how many digits are “visible” from that direction. A digit is “visible” if its view is not obstructed by a larger digit.

Digits along the arrows form a Fibonacci sequence modulo 9. Another way of saying this is that any triplet in the form ABC must follow the equation A + B = C, but values beyond 9 wrap back to 1.

For example, the digits 5 3 8 2 work because 5+3 = 8 and 3+8 = 11 = 2.