1. O.Cogis and M.Habib (1979) Nombre de sauts et graphes série-parallèles, R.A.I.R.O. Inf. Th. 13, 1, 3–18.
2. O.Cogis (1982) Problem 4.6 in Ordered Sets (I.Rival, ed.), D. Reidel, Dordrecht, p. 814.
3. M. H.El-Zahar and I.Rival (1985) Greedy linear extensions to minimize jumps, Discrete Appl. Math. 11, 143–156.
4. M.Habib (1985) Problem 8.9 in Graphs and Order (I.Rival, ed.), D. Reidel, Dordrecht, p. 576.
5. I.Rival (1983) Optimal linear extensions by interchanging chains, Proc. Amer. Math. Soc. 89, 387–394.