[1] BEHZAD M., CHARTRAND G.:
Intгoduction to the Theoгy of Graphs. Allyn and Bacon, Boston 1971,
MR 0432461
[2] CHARTRAND G., FRECHEN J. B.:
On the chromatic numbeг of permutation gгaphs. In: Proof Techniques in Gгaph Theoгy, Academic Press, New York 1969, 21-24.
MR 0250934
[3] CHARTRAND G., HARARY F.:
Planaг permutation graphs. Ann. Inst. Henri Poincare Sec. B 3, 1967, 433-438.
MR 0227041