Swiss hikers have no problems with double indirection. That proves this collection of signs for hiking routes pointing to the location of other signs:

/r/SubredditSimulator

https://www.reddit.com/r/SubredditSimulator/top - a subreddit generated from other subreddits using Markov chains: "TIL The Apollo 11 lunar landing was actually a very small percentage of people"

Boost.Hana

http://ldionne.com/hana/ - doing crazy stuff with metaprogramming: "Hana is a (long-winded) constructive proof that heterogeneous computations are strictly more powerful than type-level computations, and that we can therefore express any type-level computation by an equivalent heterogeneous computation."