tric invariant for authomorphisms of the torus. Proc. Natl. Acad. Sci. 57:1573-1576 Aftanas, L.|.,Lotova, N.V., Koshkarov, V.I., Pokrosvskaja, V.L., Popov, S.A., Makhnev, V.P (1997) Non-linear analysis of emotion EEG: calculation of Kolmogorov entropy and the principal Lyapunov exponent. Neurosci Lett