G then assigns to a terminal string an f-structure with reentrant (root E) and (root E') paths if and only if it has the form s s and s is in If all we do is unification on the top level the f-structures for the strings s 1 s 2 would still record information on the structure of their derivation.
distinct strings in {s s | s ∈ L(G 1 ) ∩ L(G 2 )} would get assigned distinct f-structures.