[1] BURRIS S.-SANKAPPANAVAR H. P.: A Course in Universal Algebra. Springer Verlag, Berlin-Heidelberg-New York, 1981. MR 0648287 | Zbl 0478.08001

[2] CHANG C. C.-KEISLER H. J.: Model Theory. (3rd ed.), Elsevier, North-Holland, Amsterdam, 1990. MR 1059055 | Zbl 0697.03022

[3] CLARKSON J. A.: Uniformly convex spaces. Trans. Amer. Math. Soc. 40 (1936), 396-414. MR 1501880 | Zbl 0015.35604

[4] ERSHOV, YU. L.-LAVROV I. A.-TAIMANOV A. D.-TAICLIN M. A.: Elementary theories. Uspekhi Mat. Nauk 20 (1965), 37-108. (Russian) MR 0186553 | Zbl 0199.03001

[5] HODGES W.: Model Theory. Cambridge Univ. Press, Cambridge, 1993. MR 1221741 | Zbl 0789.03031

[6] MENDRIS R.-ZLATOS P.: Axiomatization and undecidability results for metrizable betweenness relations. Proc. Amer. Math. Soc. (To appear). MR 1219728 | Zbl 0818.03002

[7] PITCHER E.-SMILEY M. F.: Transitivities of betweenness. Trans. Amer. Math. Soc. 52 (1942), 95-114. MR 0007099 | Zbl 0060.06408

[8] SHOENFIELD J. R.: Mathematical Logic. Addison-Wesley Reading, Mass.-1967. MR 0225631 | Zbl 0155.01102

[9] SMILEY M. F.: A comparison of algebraic, metric, and lattice betweenness. Bull. Amer. Math. Soc. 49 (1943), 246-252. MR 0008123 | Zbl 0060.06406

[10] TARSKI A.: A Decision Method for Elementary Algebra and Geometry. Univ. of Cali- fornia Press, Berkeley, 1951. MR 0044472 | Zbl 0044.25102

[11] VAUGHT R.: Remarks on universal classes of relational systems. Indag. Math. 16 (1954), 589-591. MR 0066304 | Zbl 0058.24701