To say that sellers are mutually interdependent means that business decisions are made conditioned upon expectations formed by decision makers with respect to the likely reaction of rival firms.

If Dell slashes personal computer prices, will Compaq, Gateway, Micron, et al follow suit?

If Ford offers cash rebates and low APR financing on new passenger trucks, will Chrysler, GM, Toyota, et al do the same?

How will United, American, US Air, Northwest et al react to a decision by Delta to grant frequent flyer miles to Visa card users?

If Dominoes offers "healthy" Pizza, how will Pizza Hut, Papa Johns, and the others react?