チャーチ＝チューリングのテーゼ
According to the Church–Turing thesis, any effectively calculable function is calculable by a Turing machine, and thus a set "S" is computably enumerable if and only if there is some algorithm which yields an enumeration of "S". This cannot be taken as a formal definition, however, because the Church–Turing thesis is an informal conjecture rather than a formal axiom.