This article deals with binding of a pronominal which is coindexed with an operator in an A′-position. In section 1, I will argue against the analyses of crossover phenomena by Koopman and Sportiche 1982 and Safir 1984, and propose a bidirectional condition for the pronominal to satisfy. In section 2, I will introduce the notion variable chain required for the proper functioning of pronominal binding in which intermediate traces play a crucial role. In section 3. I will present the S-indexing mechanism, which is a formal representation of an idea that a newly created S node by Chomsky-adjunction is nondistinct from an original S node. This analysis is also designed to counter May's 1985 Scope Principle and its consequences.