The Court has been applying rule of per se illegality on tie-in sales, when a
plaintiff comes to prove following factors: i) there should be two different
products; ii) a seller should set the condition to directly or actually sell a
certain product. In other words, seller coerces purchasers to buy the tied
products when purchasing the tying products; iii) a seller should have
appreciable economic power in the tying product market; iv) the tie-in sales
have substantial impact on commerce in the tying product market.