The Grammar of PENG ASP Explained Rolf Schwitter author 2021-09 text Proceedings of the Seventh International Workshop on Controlled Natural Language (CNL 2020/21) Tobias Kuhn editor Silvie Spreeuwenberg editor Stijn Hoppenbrouwers editor Norbert E Fuchs editor Special Interest Group on Controlled Natural Language Amsterdam, Netherlands conference publication schwitter-2021-grammar https://aclanthology.org/2021.cnl-1.5/ 2021-09