Constraint programming (and constraint propagation) is highly underrated.

For those not familiar with it yet, this is what's used under the hood by things like systemd: you give a bunch of constraints (ex: service A before service B, service B before service D but after service C, etc) and you get a solution (or none, but that's another story: when there are no solution, you can try to relax some constraints)

If you want to learn more, I suggest playing with Z3 from Microsoft Research: a nice tutorial is https://ericpony.github.io/z3py-tutorial/guide-examples.htm