The four-color problem/
Ore, Oystein 1899-1968.
The four-color problem/ Oystein Ore. - [1st ed.] - New York: Academic Press, 1968. - 259 p.
514 / O66f
The four-color problem/ Oystein Ore. - [1st ed.] - New York: Academic Press, 1968. - 259 p.
514 / O66f