next to (1a), (1b) and (1c) are also possible.
(i) a This is the book [NP which] I have designed [NP the covers [PP of t]] b This is the book [PP of which] I have designed [NP the covers t] c This is the book [NP the covers of which] I have designed t
In some cases, Pied Piping is obligatory, due to the Left Branch Condition.
- Ross, J.R. 1967. Constraints on variables in syntax, doctoral dissertation, MIT (published as 'Infinite syntax!' Ablex, Norwood (1986)).
- Jayaseelan, K. A. 2010. Stacking Stranding and Pied Piping: A proposal about word order, vol 13, issue 4 Syntax