Btw. to elaborate: there seems to be some troublesome sentences where a parse tree isn't just enough – you've got to have a graph. Yet, most of the linguistic p

Btw. to elaborate: there seems to be some troublesome sentences where a parse tree isn't just enough – you've got to have a graph. Yet, most of the linguistic phenomena can be parsed into tree structures. That's troublesome. It's like... there's a certain class of a parser in the brain, but then some curious sentences show the ability of overcome the "limitations" of that parser, and still they are considered grammatical.