They became part of the dirt, the land, or whatever hehehe
There's one train that has old puzzles, and another one that has complex theory equations on it! ahahahah
(one can be seen at this photo! There are others)
"So I was sitting in my cubicle today, and I realized, ever since I started working, every single day of my life has been worse than the day before it. So that means that every single day that you see me, that's on the worst day of my life."
--Peter Gibbons (Office Space)