The description of a generic function includes descriptions of the methods that are defined on that generic function by the standard. A method signature is used to describe the parameters and parameter specializers for each method. Methods defined for the generic function must be of the form described by the method signature.
F (x class)
(y t)
&optional z &key k
This signature indicates that this method on the generic function
F has two required parameters:
x, which must be a generalized instance of the class class;
and y, which can be any object
(i.e., a generalized instance of the class t).
In addition, there is an optional parameter z and a
keyword parameter k. This signature also indicates that this
method on F is a primary method and has no qualifiers.
For each parameter, the argument supplied must be in the intersection of the type specified in the description of the corresponding generic function and the type given in the signature of some method (including not only those methods defined in this specification, but also implementation-defined or user-defined methods in situations where the definition of such methods is permitted).