Apple on Thursday published a set of rules about the types of content that aren’t allowed in the iOS App Store, answering questions that have been bugging software developers and customers for years while introducing some new ambiguities.

Still, it’s an important step. By publishing the guidelines, Apple mobile customers will be able to know what they can and can’t

Animal populations headed for extinction may give the same signals seen before crashes in coral reefs, the Sahara’s climate and even stock markets.

These systems are very different, but each exhibits what’s known as “critical slowing down,” in which a loss of resilience magnifies the effect of small perturbations, which