@inbook {Heyd1995obligation,
	title = {Obligation and Supererogation},
	booktitle = {Encyclopedia of Bioethics},
	year = {1995},
	pages = {1833{\textendash}1838},
	publisher = {Macmillan},
	organization = {Macmillan},
	address = {New York},
	author = {Heyd, David}
}
