Judgment of the General Court (Fourth Chamber, Extended Composition) of 17 May 2023.#Stadtwerke Leipzig GmbH v European Commission.#Competition – Concentrations – German electricity market – Decision declaring the concentration compatible with the internal market – Action for annulment – Standing to bring proceedings – Admissibility – Obligation to state reasons – Definition of ‘single concentration’ – Right to effective judicial protection – Right to be heard – Definition of the market – Analysis period – Analysis of market power – Decisive influence – Manifest errors of assessment – Duty of diligence.#Case T-313/20.