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In mathematics, a pre-measure is a function that is, in some sense, a precursor to a ''bona fide'' measure on a given space. Indeed, one of the fundamental theorems in measure theory states that a pre-measure can be extended to a measure. ==Definition== Let ''R'' be a ring of subsets (closed under relative complement) of a fixed set ''X'' and let ''μ''0: ''R'' → () be a set function. ''μ''0 is called a pre-measure if : and, for every countable (or finite) sequence ''n''∈N ⊆ ''R'' of pairwise disjoint sets whose union lies in ''R'', :. The second property is called ''σ''-additivity. Thus, what is missing for a pre-measure to be a measure is that it is not necessarily defined on a sigma-algebra (or a sigma-ring). 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「Pre-measure」の詳細全文を読む スポンサード リンク
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