4. The method of claim 2 wherein pre-processing the input sentence comprises: splitting the input sentence into a sequence of tokens such that each token corresponds to a terminal in the terminal vocabulary of the dependency grammar; and wherein parsing the sequence of tokens comprises requiring each token to be covered by the two distinct versions of the corresponding terminal.
2. The method of claim 1 wherein the context-free grammar comprises: a terminal vocabulary that includes two distinct versions of a plurality of terminals that comprise a terminal vocabulary of the dependency grammar; and a set of productions that, for each of the plurality of terminals of the dependency grammar, generates constituents that include the left dependencies of the terminal and one of the two distinct versions of the terminal, and further generates constituents that include the right dependencies of the terminal and the other version of the terminal.