Geodesic
Decidability of the universal and positive theories of a free group
Izvestiya. Mathematics, Tome 25 (1985) no. 1, pp. 75-88 
G. S. Makanin. Decidability of the universal and positive theories of a free group. Izvestiya. Mathematics, Tome 25 (1985) no. 1, pp. 75-88. http://geodesic.mathdoc.fr/item/IM2_1985_25_1_a4/
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Voir la notice de l'article provenant de la source Math-Net.Ru

The decidability of the universal and positive theories of a free group is established. Bibliography: 3 titles.

[1] Makanin G. S., “Uravneniya v svobodnoi gruppe”, Izv. AN SSSR. Ser. matem., 46:6 (1982), 1199–1273 | MR | Zbl

[2] Lyndon R. C., “The equation $a^2b^2=c^2$ in free groups”, Michigan Math. J., 1959, no. 6, 89–95 | MR | Zbl

[3] Merzlyakov Yu. I., “Pozitivnye formuly na svobodnykh gruppakh”, Algebra i logika, 5:4 (1966), 25–42 | MR | Zbl