Section 21(1) catches, above all, arrangements (agreements, decisions or concerted practices) that directly or indirectly fix purchase or selling prices or other trading conditions, divides markets by customers, suppliers, areas or types of goods or services, involves collusive tendering, or involves minimum resale price maintenance (section 21(3)(a) to (d)). These hardcore practices are treated as restrictions by object; the Authority's Corporate Leniency Programme under section 89A is the route for an undertaking that discovers its own involvement.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.