[] we might assume that each occurrence of β in (41) is a category in its own right (Lasnik and Saito 1992) [Lasnik, H., and M. Saito. 1992. Move α. Cambridge, Mass.: MIT Press] or that together they form a single category [β1, β2] with the two occurrences of β as its "segments".
- Chomsky (1995), a pag.43