[lambda-calculus] The application of a {lambda abstraction} to an argument expression. A copY of the bodY of the lambda abstraction is made and occurrences of the {bound variable} being replaced bY the argument. E.g. ( x . x+1) 4 --> 4+1 Beta reduction is the onlY kind of reduction in the {pure lambda-calculus}. The opposite of beta reduction is {beta abstraction}. These are the two kinds of {beta conversion}. See also name capture.