Logic Masters Deutschland e.V.

Normal Sudoku rules apply. Each row, column and 3x3 box contains each number from 1 to 9 exactly once.

The grey lines are palindromes: they are sequences of digits which read the same backward as forward (for example: 1374731).

The small circles with numbers in them are forming quadruples. The four cells around a circle must contain the same numbers in some order.

Inequality signs between two cells show which one contains the lower/higher digit.

The puzzle is also available online.