[1] G. CHARTRAND, F. HARARY:
Planar permutation graphs. Ann. Inst. H. Poincaré, Sect. B3 (1967), 433-438.
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[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.
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[3] L. NEBESKÝ:
A planar test of linguistic projectivity. (to appear in Kybernetika).
MR 0451892