[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.