Problem: The timing of migration seems to be controlled primarily by changes in day length. Migrating birds navigate using celestial cues from the sun and stars, the earth's magnetic field, and probably also mental maps.
How do migrating birds navigate?
The answer is the following: celestial cues from the sun and stars

Problem: The standard PlayStation 3 version of the XrossMediaBar (pronounced Cross Media Bar, or abbreviated XMB) includes nine categories of options. These are: Users, Settings, Photo, Music, Video, TV/Video Services, Game, Network, PlayStation Network and Friends (similar to the PlayStation Portable media bar). TheTV/Video Services category is for services like Netflix and/or if PlayTV or torne is installed; the first category in this section is "My Channels", which lets users download various streaming services, including Sony's own streaming services Crackle and PlayStation Vue. By default, the What's New section of PlayStation Network is displayed when the system starts up. PS3 includes the ability to store various master and secondary user profiles, manage and explore photos with or without a musical slide show, play music and copy audio CD tracks to an attached data storage device, play movies and video files from the hard disk drive, an optical disc (Blu-ray Disc or DVD-Video) or an optional USB mass storage or Flash card, compatibility for a USB keyboard and mouse and a web browser supporting compatible-file download function. Additionally, UPnP media will appear in the respective audio/video/photo categories if a compatible media server or DLNA server is detected on the local network. The Friends menu allows mail with emoticon and attached picture features and video chat which requires an optional PlayStation Eye or EyeToy webcam. The Network menu allows online shopping through the PlayStation Store and connectivity to PlayStation Portable via Remote Play.
How is "XrossMediaBar" abbreviated?
The answer is the following: XMB

Problem: Hayek disapproved of the notion of 'social justice'. He compared the market to a game in which 'there is no point in calling the outcome just or unjust' and argued that 'social justice is an empty phrase with no determinable content'; likewise "the results of the individual's efforts are necessarily unpredictable, and the question as to whether the resulting distribution of incomes is just has no meaning". He generally regarded government redistribution of income or capital as an unacceptable intrusion upon individual freedom: "the principle of distributive justice, once introduced, would not be fulfilled until the whole of society was organized in accordance with it. This would produce a kind of society which in all essential respects would be the opposite of a free society."
What concept did Hayek dislike?
The answer is the following: social justice

Problem: In mathematics, a group is an algebraic structure consisting of a set of elements equipped with an operation that combines any two elements to form a third element. The operation satisfies four conditions called the group axioms, namely closure, associativity, identity and invertibility. One of the most familiar examples of a group is the set of integers together with the addition operation, but the abstract formalization of the group axioms, detached as it is from the concrete nature of any particular group and its operation, applies much more widely. It allows entities with highly diverse mathematical origins in abstract algebra and beyond to be handled in a flexible way while retaining their essential structural aspects. The ubiquity of groups in numerous areas within and outside mathematics makes them a central organizing principle of contemporary mathematics.
What is the name used to describe the four conditions of closure, associativity, identity and invertibility?
The answer is the following:
group axioms