nation class to element class, but never or very rarely from the
element class to the combination class in which it may be used. Thus
cross-referencing should normally be downward in a schedule of
subclasses. Search notes indicate parallel or otherwise related classes
and subclasses, and those classes and subclasses in which analogous
structures having different purposes but adapted to answer broad claims
may be found.

By arbitrary rules of arrangement such as have been referred to in the
section dealing with division and arrangement, a search may ordinarily
be definitely limited to a certain number of subclasses, even where
cross-references are not made. In such arrangement any given patent, _if
it be directed to one invention_, may be searched in the subclass within
which the definition places it or subclasses indented under it, and in
certain subclasses above, whose titles will indicate that the invention
might be included as a part of the matter defined to belong therein, but
it would never have to be searched in any subclass following and not
indented thereunder.

DIAGNOSIS TO DETERMINE CLASSIFICATION.

Each patent and each application discloses one or more means of the
useful arts (using the term "means" to cover both processes and
instruments in the sense in which it is used by Prof. Robinson), almost
always more than one, since most new means are combinations of
mechanical elements or acts. In some patents and applications the
disclosure is coextensive with that which is claimed; in others there is
matter disclosed but not claimed. The unclaimed disclosure may be as
valuable as the claimed disclosure for purposes of anticipation, and the
classification must provide for both. If the claimed disclosure belongs
in one class and the unclaimed in others, the classifier must choose
between two or more classes that one in which the patent or application
shall be classified and those into which it shall be cross-referenced.

_Claimed or unclaimed disclosure._--The claims of a patent are the
statutory indices of that which the applicant believes to be new, they
define an invention that has been searched by the Patent Office and no
anticipation discovered for it. Future action must be based on
inductions from past experience; none knows what the future lines of
search will be; the only guides for future searches are the searches of
the past; the evidence of past searches is the claims of patents; they
trace the cou