1. Def
   1. forces outside the firm which decrease AC as size of industry increases
2. types
   1. Specialisation
      1. specialized firms sell goods to firms
         1. plugs
         2. tyres
         3. windows
   2. service
      1. insurance
      2. more companies to share financial risks
   3. Education & training
      1. educate workers
      2. provided by
         1. government
         2. private sector
   4. R&D
      1. firms don't need to do their own R&D
   5. Infastructure
      1. if firm helps economy
      2. government lower
         1. communications
         2. delivery
         3. waste disposal