, to the
genus." Exhaustive division may be secured by maintaining always a
residual or miscellaneous subclass. The miscellaneous subclass
represents the remainder of the original undivided material undefined
except as the class is defined and may be accurately treated as if it
had the class title.

(6) A second rule respecting the subdivision of a class is: "The
constituent species must exclude each other." That is, the divisions or
subclasses must not overlap. (See exception in Rule 8.)

Example: If a number of balls of several different
materials, several different conformations, or
constructions, several different colors, were to be divided
into glass balls, hollow balls, and red balls, this rule
would be violated, because some balls would be glass,
hollow, and red.

(7) A third rule respecting subdivision is: "The divisions must be
founded on one principle or basis." The application of this rule will
generally form divisions that do not overlap. (See exception in Rule 8.)

Example: If a number of balls of several different
constructions, several different materials, and several
different colors were to be classified so as to provide a
place for each kind of characteristic, they should be
divided first, for example, according to construction into
hollow balls and solid balls, each of these according to
materials into glass balls, rubber balls, metal balls,
wooden balls, etc., and each of the latter into red balls,
blue balls, green balls, etc.

(8) When it is found that division into overlapping subclasses and on
different characteristics is a lesser evil than an unwieldy number of
subclasses that would otherwise result, then those subclasses based on
characteristics deemed more important for purposes of search should
precede in the list of subclasses those based upon characteristics
deemed less important. (See Rule 6.)

(9) In arrangement of subclasses or subdivisions the miscellaneous
groups containing material not falling within any of the specifically
entitled subclasses, should stand first; those subclasses defined by
effect or special use should precede those defined by function or
general use; those containing matter that is related to the matter of
other subclasses as whole to part should precede those subclasses that
contain the part; and those defined by a characteristic deemed more
important or significant for search purposes should precede those
defi