Judgment of the General Court (Fifth Chamber, Extended Composition) of 20 December 2023.#Stadtwerke Hameln Weserbergland GmbH, formerly GWS Stadtwerke Hameln GmbH v European Commission.#Competition – Concentrations – German electricity and gas markets – Decision declaring a concentration compatible with the internal market – Obligation to state reasons – Concept of ‘single concentration’ – Right to effective judicial protection – Right to be heard – Definition of the market – Analysis period – Assessment of the effects of the transaction on competition – Manifest errors of assessment – Commitments – Duty of diligence.#Case T-58/21.