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In mathematics, especially order theory, a prefix ordered set generalizes the intuitive concept of a tree by introducing the possibility of continuous progress and continuous branching. Natural prefix orders often occur when considering dynamical systems as a set of functions from ''time'' (a totally ordered set) to some phase space. In this case, the elements of the set are usually referred to as ''executions'' of the system. The name ''prefix order'' stems from the prefix order on words, which is a special kind of substring relation and, because of its discrete character, a tree. == Formal definition == A prefix order is a binary relation "≤" over a set ''P'' which is antisymmetric, transitive, reflexive, and downward total, i.e., for all ''a'', ''b'', and ''c'' in ''P'', we have that: *''a ≤ a'' (reflexivity); *if ''a ≤ b'' and ''b ≤ a'' then ''a'' = ''b'' (antisymmetry); *if ''a ≤ b'' and ''b ≤ c'' then ''a ≤ c'' (transitivity); *if ''a ≤ c'' and ''b ≤ c'' then ''a ≤ b'' or ''b ≤ a'' (downward totality). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「prefix order」の詳細全文を読む スポンサード リンク
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