Trapping Rain Water (simple TLA spec)

[Viktor Danylenko]

Hi All, 

As part of my TLA+ learning, I wrote a spec for a Leetcode problem (https://leetcode.com/problems/trapping-rain-water/description/)

It simple to the point I doubt its usefulness, but I would still appreciate any feedback or suggestion if you have minute to review it. The spec can be found here: https://github.com/vdanylenko/tla/blob/main/trap_water.tla

Thanks you!

Viktor