An article discussing three valuable programming language features: flow typing (demonstrated in Crystal and TypeScript) that allows variables to change types while maintaining static safety, borrow checking in Rust that prevents data races at compile-time through elegant reference rules, and contract programming in D that provides syntactic support for invariants and pre/post-conditions.
Necker's 1832 observations document optical phenomena witnessed in Switzerland, including a notable effect observed when viewing figures of crystals or geometrical solids, now known as the Necker cube illusion.