Comparative Similarity in Branching Space-Times

My aim in this paper is to investigate the notions of comparative similarity definable in the framework of branching space-times A notion of this kind is required to give a rigorous Lewis-styli semantics of space-time counterfactuals In turn, the semantical analysis is needed to decide whether the recently proposed proofs of the non-locality of quantum mechanics are correct From among the three notions of comparative similarity I select two which appear equally good as far as their intuitiveness and algebraic properties are concerned However, the relations are not transitive, and thus cannot be used in the semantics proposed by Lewis (J Philos Log 2 418-446, 1973) which requires transitivity Yet they are adequate for the account of Lewis (J Philos Log 10 217-234, 1981)