Existence of Lyapunov functions of variable sign for linear extensions of dynamical systems on a torus
English version (Springer): Ukrainian Mathematical Journal 42 (1990), no. 12, pp 1548-1552.
Citation Example: Kulik V. L. Existence of Lyapunov functions of variable sign for linear extensions of dynamical systems on a torus // Ukr. Mat. Zh. - 1990. - 42, № 12. - pp. 1713–1717.
Full text