Puzzle #251 - Opposition (Non-Consecutive Skyscrapers)

I'm going to be trying to make daily puzzle posts during December again, and specifically I'll be aiming for a different variant puzzle every day through Christmas. Will I succeed? I hope so! First up is a puzzle I prepared earlier, a non-consecutive Skyscrapers puzzle. Solve as a standard Skyscrapers puzzle, with the additional rule that numbers differing by one may not be orthogonally adjacent. This 6x6 turned out very difficult to construct, after a completely unfair 7x7 and several failed attempts on larger grids.

puzz.link interface

(thanks to gravel and Bryce for pointing out the original 2 placements left 2 solutions. The puzzle has been fixed twice and definitely has one solution now.)

And for fun, here's the unfair puzzle. If you're just trying to find *a* solution it should be doable, but proving it's the only solution required me to make several 3-level case distinctions. It's an elegant design, however, and honestly surprising that it works.

puzz.link interface