['he', 'know', 'EmptyParameter', 'contents', 'about']
['<PRP>', 'comprehend-87.2', 'EmptyParameter', "Synset('database.n.01')", 'about']
He already knows about the contents of the letter.
<PRP> already knows about the Synset('database.n.01') of the Synset('written_symbol.n.01').