Arrow’s (im)possibility theorem is one of the most famous and important contri- butions in economics. It concerns the difficulty to aggregate a set of individual preferences, given as rankings of a set of available alternatives, into a unique social preferences ranking via a social welfare function, or into a unique social choice. Arrow proves that in a specific framework, it is impossible to find a social welfare function which simultaneously satisfies four conditions: universal domain, weak Pareto principle, independence of irrelevant alternatives, and no dictator. Our no- tice presents this theorem, one of its proofs, and, we hope, invites the reader to discover social choice theory
