[1] G. CHARTRAND, F. HARARY: Planar permutation graphs. Ann. Inst. H. Poincaré, Sect. B3 (1967), 433-438. MR 0227041 | Zbl 0162.27605

[2] G. CHARTRAND, J. B. FRECHEN: On the chromatic number of permutation graphs. in: Pcoof Techniques in Graph Theory (Ed. F. Harary), Academic Press, New York and London 1969, pp. 21-24. MR 0250934 | Zbl 0199.59401

[3] L. NEBESKÝ: A planar test of linguistic projectivity. (to appear in Kybernetika). MR 0451892