Possible Clues:

• Dominance of two suppliers
• Dominance by just two companies
• Twin powers in charge here, properly including work with oxygen
• Picked up work in noisy yard for couple of suppliers
• Limited cartel
• Market dominance by two companies
• Where two companies dominate a market
• Form of market domination, as might be expected, restricting work to ring
• Limited competition correctly including piano in two rounds