In the year 1990 in ECAI, who are the authors that published research papers about Planning knowledge?
In European Conference on Artificial Intelligence in 1990, who are the authors that published papers about Planning knowledge?
SELECT DISTINCT ?answer WHERE { <https://dblp.org/rec/conf/ecai/Yang90> <https://dblp.org/rdf/schema#authoredBy> ?answer . <https://dblp.org/rec/conf/ecai/Yang90> <https://dblp.org/rdf/schema#publishedIn> 'ECAI' . <https://dblp.org/rec/conf/ecai/Yang90> <https://dblp.org/rdf/schema#yearOfPublication> '1990' }
<https://dblp.org/rec/conf/ecai/Yang90>