Even extracting binarized fragments (depth 1 and 2, with one order of parent annotation) gives us 0.75 million rules, and, practically, we would need fragments of greater depth.
g. each derivation d in g has a nonempty set of corresponding derivations {d I } = π −1 (d) in g I , because fragments f in d correspond to multiple fragments f I in g I that differ only in their indexed symbols (one f I per occurrence of f in B).