@incollection{szasz93,
	author = {Nora Szasz},
	booktitle = {Logical Environments},
	editor = {{G\'erard} Huet and Gordon Plotkin},
	publisher = "Cambridge University Press",
	year = {1993},
	pages = {317-338},
	title = {A Machine Checked Proof that {Ackermann's} Function is not Primitive Recursive}}
