Logic Masters Deutschland e.V.

Can you please help me? I have solved this Sudoku, but I completely forgot to take all the rules into consideration.

Please help me empty the sudoku grid so I can start again.

Puzzle Link:

Penpa+: Contains the full puzzle
Sudokupad: For those only interested in the regular solve

Rules:

Empty the sudoku grid by removing the digits 1-9 in the correct order so that after the removal of a digit (all of a single digit (for example: all 1's or all 2's)) the given constraint is satisfied. Empty cells should be coloured black for an answer check.

After each removal, the given constraint will have to be satisfied (constraint 1 after the first digit, constraint 2 after the second digit and so on), disregarding the old constraints. Empty cells are ignored for the constraint, unless stipulated otherwise.

Constraint 1: Sandwich: The clues outside the grid give the total sum of digits that fall between the 1 and the 9 of the clue’s row or column.

Constraint 2: Skyscrapers: Each digit in the grid represents the height of its cell. Taller cells obstruct the view of shorter ones behind them. Clues outside the grid divided by 2 give the number of cells visible from that vantage point in the clue's row or column.

Constraint 3: Palindrome: The grey line is a Palindrome line, digits on this line must read the same forwards and backwards. (The entire line does not necessarily have to be filled (1-empty-2-1-empty is valid, as it reads 1-2-1)).

Constraint 4: Renban: The purple line is a Renban line, digits on this line must form a non-repeating consecutive set of digits. (The entire line does not necessarily have to be filled (1-2-3-4 on a 7 line is valid)).

Constraint 5: Even/odd: The digits on the grey squares are either all even or all odd.

Constraint 6: Killer cages: Digits in cages do not repeat and sum to the number in the top left corner of the cage.

Constraint 7: Thermometer: The grid contains Thermometers, digits on a thermometer increase from the bulb end.

Constraint 8: Greater than: Inequality signs point towards the lowest digit of the two cells. (Empty cells can be considered as 0).

Constraint 9: Empty: Remove the remaining digit from the grid.