Collections have indexed access to members.
Observation targets implement -isEqual: and -hash.

They also call the correct method when being removed, fixing a crash.
Collection view controllers pass their segues to a delegate.

This is used to set up a delegate/dataSource for the repos list.
Monadic recursion uses the predicate at more than just the first iteration.
The persistence controller uses a predicate to stop on nil contexts.
Corrects insertions using the wrong index path.
Change tracking is greedy.
Uniques Person instances by userName.