The macro define-method-combination defines new forms of method combination. It provides a mechanism for customizing the production of the effective method. The default procedure for producing an effective method is described in Determining the Effective Method. There are two forms of define-method-combination. The short form is a simple facility while the long form is more powerful and more verbose. The long form resembles defmacro in that the body is an expression that computes a Lisp form; it provides mechanisms for implementing arbitrary control structures within method combination and for arbitrary processing of method qualifiers.