P-disjunctive omega-languages
An ω-language over a finite alphabet X is a set of infinite sequences of letters of X. An ω-language L is P-disjunctive if Pω, L is the equality, where Pω, L is the congruence on X* introduced by L. We prove that L contains a P-disjunctive ω-language if and only if L is P-dense. In order to determine whether a given ω-language is P-disjunctive or not, the concept of P-disjunctive domains is defined in this paper. And it is showed that P-disjunctive domains are equivalent to disjunctive domains.