Just one message to the developer: FUUUUUUUUUUUUUUUUUUUUUUUU
This is really easy I mean there's no mental challenge, there are obvious *fill the whole area*s and they trigger other numbers as filled so you just "X" the remaining areas (like a 6 next to 9) and keep doing that
But overall process is really brain tiring and ONE mistake you'll have to restart