I've wanted to compile a list of canonical simplified problem settings in various fields. Their longevity is interesting to me. Things like the relativistic b

I've wanted to compile a list of canonical simplified problem settings in various fields. Their longevity is interesting to me. Things like the relativistic boxcars in physics, the urns and balls in probability (http://www.arcaneknowledge.org/science/ehrenfest.html http://www.arcaneknowledge.org/science/ehrenfest.html), the teapot, Lena, blocks-world in AI.