We thus consider two path simplifications as well: • compressed: only the source, target, and root nodes are preserved in the path (so the path above becomes [VBP ↑ S ↓ NP]) • POS class clusters: rather than distinguish, for example, between different tenses of verbs in a path, we consider only the first letter of each NT.
• Given a Levenshtein alignment between altered rules, the most common changes within a given NT phrase are detailed in column five of Table 1.