LATIN SQUARE - Place the digits 1-9 once each in every row and column. LATIN SQUARES - Subdivide the grid into smaller latin squares, which can be any size except 1×1. An N×N latin square contains exactly N unique digits selected from 1 to 9 (such that those N unique digits do not repeat in any row/column of their latin square). Latin squares with the same size may not have the same digit in the same relative position. (Eg if a 4×4 latin square has a 7 in its upper left corner, no other 4×4 latin square may have a 7 in its upper left corner). Digits on an arrow sum to the digit in the attached circle.