As an American, I spend far too much time thinking about urban design. This puzzle prompts thoughts of apartment buildings in Barcelona. They didn’t turn out the way Ildefons Cerda planned, but they’re certainly distinctive.

Sometimes the most difficult part of solving a puzzle is deciding which colors to use. Do you color pairs, individual digits, or high/low? I use yellow for low and sky blue for high, personally This is a hint that coloring will be helpful with this puzzle, and possibly more than one kind!

Lockout Lines can be counter-intuitive, to a point. Instead of the digits between two numbers, you want the digits not between two numbers. Normally you can work out “these are high, so those are low,” but with lockout lines, you could end up with both high and low digits together.

These arrows keep aiming for those quadruples, but missing. They’ve got the aim of Star Wars stormtroopers. Also, this is the 100th puzzle posted to this blog! (Internally, it’s puzzle 2630.)

Every digit on every renban line go into its own separate compartment, since these short renban lines all fit entirely within… oh, there are a couple of long lines too. Maybe they’re important.

It’s so easy to get started. So many dots arranged so carefully. And then… well, this cell, let’s make it orange, and then we need three more orange cells in these three rows, but we also need two green cells in two of those rows, so…

I see your 159, and raise you 3 and 7. My hand is strong, so I’m willing to keep raising if I have to. This one also had some testing contoversy, with difficulty estimates and solve times ranging widely.

It’s a big one, and it’s anchored by Gravity Cages at the bottom. While these cages don’t directly affect anything else in the puzzle, I like to imagine they’ll combine to form a black hole, pulling everything in all four grids into a single cell.

When the arrow points to the bottom right, the cage is a Young Tableau, but something’s gone strange in this puzzle, and gravity seems to be pulling every which way. Some cages are upside-down or reversed or both, but the arrow always points in the direction of strongest gravitational attraction.

With the largest digit in the bottom right corner, these are also known as Young Tableaux. I’ve added an indicator arrow both as a reminder of the Young Tableaux constraint, and as a hint that future Gravity Cages might not always have the arrow point in that direction.