A method is uniquely identified by name and index,
or by name and parameter restrictions. Each method for a generic
function is assigned a unique integer index within the group of
all methods for that generic function. Thus, if a new method is
defined which has exactly the same name and parameter restrictions
as another method, CLIPS will automatically replace the older
method. However, any difference in parameter restrictions
will cause the new method to be defined in addition to
the older method. To replace an old method with one that has different
parameter restrictions, the index of the old method can be explicitly
specified in the new method definition. However, the parameter
restrictions of the new method must not match that of another
method with a different index. If an index is not specified, CLIPS
assigns an index that has never been used by any method (past
or current) of this generic function. The index assigned by CLIPS
can be determined with the list-defmethods
command (see section 13.10.4).