Case T-319/20: Judgment of the General Court of 17 May 2023 — GGEW v Commission (Competition — Concentrations — German electricity market — Decision declaring the concentration to be compatible with the internal market — Action for annulment — Standing to bring proceedings — Admissibility — Obligation to state reasons — Concept of a ‘single concentration’ — Right to effective judicial protection — Right to be heard — Definition of the market — Period of analysis — Analysis of market power — Decisive influence — Manifest errors of assessment — Duty of diligence)