A precedence relation over members of a set, that is, a relation that indicates which members come before others. Mathematically, orderings are acyclic and usually transitive. Thus, if A comes before B and B comes before C, then (by transitivity) A comes before C. Orderings are often used in constructing outlines, narratives, and teaching sequences. For example, topics in a textbook are typically arranged in an order so that a reader will first cover the prerequisites for a topics before encountering the topic itself. See also partial ordering and complete ordering.