This avoids introducing discourse units that were not part of the original annotation, which a preliminary binarization of trees would have induced.
rST-Parseval considers approximately twice as many nodes as the original Parseval would on binarized trees (at most 2n − 2 nodes for n EDUs, compared to n − 1 attachments in a binary tree), and the relation labels of most nuclei are redundant with the nuclearity of a node and its sister (SPAN for a nucleus whose sisters are satellites, and the same label as its sisters for a nucleus whose sisters are nuclei).