Normal Sudoku rules apply. The two gray fields represent the two ends of a snake, i.e. a path that is one cell wide and does not touch itself orthogonally or diagonally. The sudoku grid without the cells of the snake must be a single connected area. The clues at the edge indicate how many 90 degree bends the snake has in the corresponding row or column. Here "0" means that the snake in the respective row or column contains no 90 degree bend, and "+" means that it makes at least one 90 degree bend in the row or column. The numbers on this snake form a palindrome. The comparison symbols between two cells indicate which of the two cells contains the larger digit.