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In mathematics, a covering system (also called a complete residue system) is a collection : of finitely many residue classes whose union contains every integer. == Examples and definitions == The notion of covering system was introduced by Paul Erdős in the early 1930s. The following are examples of covering systems: : and : and : A covering system is called ''disjoint'' (or ''exact'') if no two members overlap. A covering system is called ''distinct'' (or ''incongruent'') if all the moduli are different (and bigger than 1). A covering system is called ''irredundant'' (or ''minimal'') if all the residue classes are required to cover the integers. The first two examples are disjoint. The third example is distinct. A system (i.e., an unordered multi-set) : of finitely many residue classes is called an -cover if it covers every integer at least times, and an ''exact'' -cover if it covers each integer exactly times. It is known that for each there are exact -covers which cannot be written as a union of two covers. For example, : : is an exact 2-cover which is not a union of two covers. 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「covering system」の詳細全文を読む スポンサード リンク
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