完美的竞争：

完全竞争市场的特征by the presence of many buyers and many sellers with both the parties being mere price takers, presence of perfect knowledge, homogeneous product and free entry and exit from the market.

Under such of a setting a firm faces a horizontal demand curve and decides to sell whatever it can at the given market price. Being a profit maximiser, the firm in the short-run, chooses to sell that amount of output for which the p = MC. As long as p> min AVC, the firm earns supernormal profit by producing and selling in the market.

在长期出现的情况下，由于自由进入和退出市场，该公司的长期均衡发生在LAC的最低点，在lac的最低点上，P = min lac，从而扫除了超级利润。因此，从长远来看，由于自由进入和退出市场的现象，这些公司也只是破坏了。