Overt Comp constraint on stacked relatives

Stacked relatives of the kind in ((281)) are handled.

(280)0(280

(281)

[[the book [that Bill likes]] [which Mary wrote]] 

There is a constraint on stacked relatives: all but the relative clause closest to the head-NP must have either an overt Comp or an overt NP_w. Thus ((282)) is ungrammatical.

(281)0(281

(282)

*[[the book [that Bill likes]] [Mary wrote]] 

Again, no good way of handling this constraint is known to us currently.