# SlitherLITS: Don't colour outside the lines

This puzzle is part of the Monthly Topic Challenge #13: Variety Slitherlinks.

• Draw a single, non-intersecting loop that only consists of horizontal and vertical segments between the dots.
• Numbers inside a cell indicate how many of the edges of that cell are part of the loop.
• Shade the interior of the loop so that every cell is part of an L, I, T, or S tetromino.
• No 2×2 group of cells can be entirely shaded.
• When two tetrominoes share an edge, they must not be of the same type (L, I, T, or S), regardless of rotations or reflections.

Should be solvable by hand with no guessing/backtracking.

Penpa link (If you want the Penpa automated checker to work, Use Green for the loop, and (DG, GR, LG, BK) for shading.)

What a wonderful puzzle!

I started with typical sli-li deductions but had to use all the rules to disambiguate.

e.g.,:

The adjacency restriction helps disambiguate L and S.

Solution:

How I started out:

Got this far with standard slitherlink (I think?)

These squares must be part of an L with long tail up or down due to T adjacency. The x in the upper left is needed to avoid a region with area 1 or 3.

• Nicely done. Can you add some more detail on your solve path. I'm curious to see how close it was to the intended route, or if there are shortcuts I missed when testing/tweaking.
– fljx
Commented Aug 3, 2023 at 16:01
• @fljx Is it fine if I add an answer with more detail and explanation? Commented Aug 3, 2023 at 16:45
• Sure. I'll try and retrace my steps and update later. Commented Aug 3, 2023 at 17:08
• @fljx, I'm sorry. I deleted most of my solving path while trying to highlight one step in Penpa...still getting the hang of it. I added some of my initial steps, at least. Commented Aug 3, 2023 at 17:52
• @n1000 When using Penpa, I make heavy use of the "clone" button. It does what it says, and gives you a clone of your current position in a new tab, complete with undo/redo history. I find it very useful for creating an instant backup if I'm about to make a potentially destructive change.
– fljx
Commented Aug 3, 2023 at 19:14