Under each valid heading, other headings representing concepts on a level immediately above in the hierarchy are listed as BT (Broader term), except when the heading in question represents the "top term" in the hierarchy, or when the broader term cannot be readily identified. Other exceptions include headings for geographic regions, family names, and inverted headings qualified by names of languages, nationalities, ethnic groups, or terms that designate time periods, when the only appropriate BT is the identical heading without the qualifier. When a heading belongs to more than one hierarchy, multiple BT references may be made. In complex situations such as compound headings, prepositional phrase headings, and headings with subdivisions, BT references not representing true hierarchical relationships are made in selective cases. Examples

10.21 References

See also:

10.2 Hierarchical relationships