@ARTICLE {
	AUTHOR = "Pablo Barcel{\'o} and Miguel Romero and Thomas Zeume",
	TITLE ="A More General Theory of Static Approximations for Conjunctive Queries",
	JOURNAL = "Theory of Computing Systems (ToCS)",
	VOLUME = "64",
	PAGES = "916-964",
	YEAR = "2020",
	PUBLISHER = "Springer-Verlag",
	ADDRESS = "Berlin/Heidelberg, Germany",
	ISSN ="1433-0490",
	}