One or more headings may be assigned to a work on a single topic, depending on whether a co-extensive heading exists. The heading that exactly represents the content, if it exists or can be established, is assigned to a work on a single topic. Form subdivisions, many of which are free-floating, are used when appropriate; they may be assigned under all types of headings--personal names, corporate names, meetings and conferences, uniform titles, geographic headings, and topical headings. If the topic of the work being cataloged is not represented in the Subject Authority File, and for various reasons it is impossible or impractical to establish the concept as a new heading, a more general heading or several related headings, whichever designates most closely the topic of the work, are assigned. Examples

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26.0 Number of headings