[Roonerelli]

there are two hard things in computer science: cache invalidation, naming things, and off-by-one errors

[peteretep]

there are three hard things concurrency, in computer science: cache invalidation, naming things, and off-by-one errors

[jph]

what's the name for the four hard things concurrency, in computer science: cache invalidation, off-by-one errors, naming things, and whatever the last one is called?

[Roonerelli]

http://martinfowler.com/bliki/TwoHardThings.html