Inequality Sudoku
Place a digit from 1 to 9 into each of the empty squares so that each digit appears exactly once in each row, column and 3x3 box. There are given symbols of ‘greater than’ (>) or ‘less than’ (<) on the common line of the two adjacent cells.
Arrow Sudoku
Place a digit from 1 to 9 into each of the empty squares so that each digit appears exactly once in each row, column and 3x3 box. The number in a circle is the sum of the digits which are covered by its arrow.
Kropki Sudoku
Place a digit from 1 to 9 into each of the empty squares so that each digit appears exactly once in each row, column and 3x3 box. The white dots indicate all the adjacent/neighboring cells in which the difference between the two cells is 1. The black dots indicate all the adjacent cells in which one digit is the double of the other one. The dot between two cells with digits 1 and 2 has any of these two colors.
Anti-knight Sudoku
Place a digit from 1 to 9 into each of the empty squares so that each digit appears exactly once in each row, column and 3x3 box. The same numbers are not chess-knight move connected.
