 Once the table of possibilities has been determined, a crucial tactic to solve the puzzle involves "AB elimination", in which subsets are identified within a row whose range of values can be determined.For example, if the first two squares within a row must contain 1 or 2, then these numbers can be excluded from the remaining squares.Similarly, if the first three squares must contain 1 or 2; 1 or 3; and 1 or 2 or 3, then those remaining must contain other values (4 and 5 in a 5×5 puzzle).