[1] M. Behzad G. Chartrand: Introduction to the Theory of Graphs. Allyn and Bacon, Inc., Boston 1971. MR 0432461

[2] G. Chartrand F. Harary: Planar permutation graphs. Annales de l'Institut Henri Poincaré 3 (1967), Section B, 433-438. MR 0227041

[3] S. Marcus: Algebraic Linguistics; Analytical Models. Academic Press, New York 1967. MR 0225610 | Zbl 0174.02402

[4] L. Nebeský: Algebraic Properties of Trees. Karlova universita, Praha 1969. MR 0274210

[5] L. Nebeský: A planar test of linguistic projectivity. Kybernetika 8 (1972), 351-354. MR 0451892

[6] L. Nebeský: Projectivity in linguistics and planarity in graph theory. Prague Studies in Mathematical Linguistics 5 (submitted).

[7] P. Novák: Postscript. [4], 83-95.

[8] L. Uhlířová: On the non-projective constructions in Czech. Prague Studies in Mathematical Linguistics 3, Academia, Praha 1972, pp. 171-181.