is a composition tool for writing scholastic works, in which the sources, and the writer's notes from the sources, are integrated into the outline for ease of reference during the writing process. A software program designed for processing outlines is called an outliner. Types of outlines Outlines are differentiated by style, the inclusion of prefixes, and specialized purpose. There are also hand-written outlines (which are highly limited in utility), and digitized outlines, such as those contained within an outliner (which are much more useful). By style There are two main styles of outline: sentence outlines and topic outlines. A sample topic outline application: An outline of human knowledge Propædia is the historical attempt of the Encyclopædia Britannica to present a hierarchical "Outline of Knowledge" in a separate volume in the 15th edition of 1974. The Outline of Knowledge was a project by Mortimer Adler. Propædia had three levels, 10 "Parts" at the top level, 41 "Divisions" at the middle level and 167 "Sections" at the bottom level, numbered, for example, "1. Matter and Energy", "1.1 Atoms", "1.1.1. Structure and Properties of Sync”. By prefixing used A feature included in many outlines is prefixing. Similar to section numbers, an outline prefix is a label (usually alphanumeric or numeric) placed at the beginning of an outline entry to assist in referring to it. Bare outlines Bare outlines include no prefixes. Alphanumeric outline An alphanumeric outline includes a prefix at the beginning of each topic as a reference aid. The prefix is in the form of Roman numerals for the top level, upper-case letters (in the alphabet of the language being used) for the next level, Arabic numerals for the next level, and then lowercase letters for the next level. For further levels, the order is started over again. Each numeral or letter is followed by a period, and each item is capitalized, as in the following sample: Some call the Roman numerals "A-heads" (for "A-level headings"), the upper-case letters, "B-heads", and so on. Some writers also prefer to insert a blank line between the A-heads and B-heads, while often keeping the B-heads and C-heads together. If more levels of outline are needed, lower-case Roman numerals and numbers and lower-case letters, sometimes with single and double parenthesis can be used, although the exact order is not well defined, and usage varies widely. The scheme recommended by the MLA Handbook, and the Purdue Online