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出典:『Wikipedia』 (2011/05/23 17:19 UTC 版)

英語による解説

引用

In abstract algebra, the free monoid on a set A is the monoid whose elements are all the finite sequences (or strings) of zero or more elements from A. It is usually denoted A^∗. The identity element is the unique sequence of zero elements, often called the empty string and denoted by ε or λ, and the monoid operation is string concatenation. The free semigroup on A is the subsemigroup of A^∗ containing all elements except the empty string. It is usually denoted A⁺.