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#### 3.4.7 Defsetf Lambda Lists

A defsetf lambda list is used by defsetf.

A defsetf lambda list has the following syntax:

lambda-list ::=({var}* `[`&optional {var | (var [init-form [supplied-p-parameter]])}*`]` `[`&rest var`]` `[`&key {var | ({var | (keyword-name var)} [init-form [supplied-p-parameter]])}* pt [`&allow-other-keys`]`]` `[`&environment var`]`

A defsetf lambda list can contain the lambda list keywords shown in Figure 3–19.

      &allow-other-keys  &key       &rest
      &environment       &optional

      Figure 3–19: Lambda List Keywords used by Defsetf Lambda Lists

A defsetf lambda list differs from an ordinary lambda list only in that it does not permit the use of &aux, and that it permits use of &environment, which introduces an environment parameter.