The notion "local control" must be made precise. One case of "local control" will be agreement in pro-drop languages. Recall that the element AGR is coindexed with the subject that it governs. We have assumed this coindexing to be distinct from that of the binding theory, say, co-superscripting [...] In the pro-drop languages, we take such coindexing to serve as "local control" in the required sense. A second case of "local control" is coindexing with an adjacent "wh"-phrase or trace of a "wh"-phrase in COMP.
- Chomsky (1993), a pag.241