The theory that some rivers have sources on the rainier sides of mountain ranges and gradually erode backward until the ranges are cut through.

Retreat of the sea from land areas, and the consequent evidence of such withdrawal.

A mental state and a mode of adjustment to difficult and unpleasant situations, characterized by behavior of a type that had been satisfying and appropriate at an earlier stage of development but which no longer befits the age and social status of the individual.

Given two stochastically dependent random variables, regression functions measure the mean expectation of one relative to the other.