 such that whenever \(Txy\) and \(Rxu\) hold, there exists \(v\) such that \(Tuv\) and \(Syv\) hold, and whenever \(Txy\) and \(Ryv\) hold, there exists \(u\) such that \(Tuv\) and \(Rxu\) hold. We can then define the membership relation: the set represented \(B, b, S\) is a member of the set represented by \(A, a, R\) iff there exists \(a_1\) such that \(Ra_1a\) and \(A, a_1, R\) and \(B, b, S\) are bisimilar.