Case T-399/16: Judgment of the General Court of 28 May 2020 — CK Telecoms UK Investments v Commission (Competition — Concentrations — Wireless telecommunications — Retail market for mobile telecommunication services — Market for wholesale access and call origination on public mobile networks — Acquisition of Telefónica Europe by Hutchison — Decision declaring the concentration incompatible with the internal market — Oligopolistic market — Significant impediment to effective competition — Non-coordinated effects — Burden of proof — Standard of proof — Market shares — Effects of the merger on prices — Quantitative analysis of upward pricing pressure — Close competitors — Important competitive constraint — Important competitive force — Network-sharing agreements — Level of concentration — Herfindahl-Hirschmann Index — Error of law — Error of assessment)