What-NP
fused relative에서 what은 상위 clause의 constituent(antecedent)로서의 function과 relative clause의 constituent(relativized element)로서의 function을 동시에 수행한다.
what proved to be the oldest fossil whale
- NP
- head(pronoun): what
- modifier(relative clause): proved to be the oldest fossil whale
- head(V): proved (be-passive)
- complement(to-infinitival clause): to be the oldest fossil whale