Logic Masters Deutschland e.V.

This puzzle was inspired by certain ideas that I discovered while solving Shintaro's brilliant puzzle, Rule of Thirds, along with some discussions I had with him afterwards.
Shintaro also gets further credit for testing this puzzle, and suggesting the name.

Note: This puzzle is very difficult, but it can be solved logically.
For easier puzzles with the same ruleset, some introductory puzzles (with an example) can be found here.

Rules:

• Divide the grid into orthogonally connected regions.
  A region must contain the numbers from 1 to N once each, where N is the largest number in the region.
• Regions may also contain empty cells.
• A ? stands for an unknown number.

Penpa link: Click Here