Hi, glad you're enjoying the game. It's so long since I coded it I've forgotten how to complete the levels sorry. Rest assured every level is possible though. I think you can also move onto Set Five if you've completed 80% of Set Four if you'd like a break from that puzzle.
Nah, my OCD doesn't allow me, to proceed to the next levels, lol. Having a break from it today, continuing "BrainBreak (lvl061 atm, hehe) and i'll give it a retry tomorrow.
But that level (Set four, level ten), is truly something, for nightmares, lol.
