Was a paper not not co-authored by Xiaoyan Sun and Haifeng L.?
Didn't X. Sun and Haifeng L. not co-author a paper?
ASK { ?x <https://dblp.org/rdf/schema#authoredBy> <https://dblp.org/pid/13/1574-1> . ?x <https://dblp.org/rdf/schema#authoredBy> <https://dblp.org/pid/84/33> }
<https://dblp.org/pid/13/1574-1> <https://dblp.org/pid/84/33>