<PI> (Or "contraction") The process of transforming an expression according to certain reduction rules. The most important forms are beta reduction (application of a lambda abstraction to one or more argument expressions) and delta reduction (application of a mathematical function to the required number of arguments).
An evaluation strategy (or reduction strategy), determines which part of an expression (which redex) to reduce first. There are many such strategies.
See graph reduction, string reduction, normal order reduction, applicative order reduction, parallel reduction, alpha conversion, beta conversion, delta conversion, eta conversion.
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