def _purge_unreachable(self, key):
dels = []<EOL>for p in self:<EOL><INDENT>if dominates(key, p):<EOL><INDENT>dels.append(p)<EOL><DEDENT><DEDENT>for k in dels:<EOL><INDENT>_, idxs = find_in_tree(self.root, k, perfect=True)<EOL>del_by_idx(self.root, idxs)<EOL><DEDENT>
Purge unreachable dominated key paths before inserting a new key
path.