“…WE appears on both ROOT-S and S, since they may be either statements or questions, but does not appear on REL-S, since it has no option. REL-S contains a single TRACE flag, to bind the relativized position within the clause to the head of the relative, while S has two, to provide the correct links between extracted WH phrases and their traces via the well-known difference list [73] or "trace-threading" [24] mechanism. ROOT-S has no need for this feature, since, by definition, there is no place external to a matrix clause to bind a trace.…”