22) Perfect Competition - This is the 2d plateau on the journey. Average total cost is average cost, not total cost (it is called ATC because it includes fixed and variable costs). Exit and entry occur depending on whether AC is below or above MC=MR, respectively. The perfect competition model is about as complex as a Rubik Cube - it moves prismatically according to unrealistic (abstract) assumptions, is connected to the economy via statistical data and constrains thinking.