@book{533103,
	author = {Polya, George, and Tarjan, Robert E.},
	title = {Notes on introductory combinatorics /},
	publisher = {Birkhauser,},
	year = {c2010},
	address = {Boston :},
	note = {"Reprint of the 1983 edition--On title page."},
	url = {https://link.springer.com/10.1007/978-0-8176-4953-1}
}