In 2011, Liangrui Tang, Lin Zhao, and Qin Zhang proposed a new four-dimensional system 
which produces an interesting attractor for the parameter values as a=55, b=25, c=40, d=13, (e=23, and f=8. Initial conditions can be as x = 0, y = 1, z = 0 and w=1. Two planes projections of the attractor are shown in Fig. 1. Contrary to what was initially claimed, this attractor is not hyperchaotic and has a single positive Lyapunov exponent .
This is confirmed by the one-dimensional first-return map to a Poincaré section which is shown in Fig. 2.
 L. Tang, L. Zhao & Q. Zhang, A novel four-dimensional hyperchaotic system, In : \it Applied Informatics and Communication, Springer-Verlag, pp. 392-401, 2011.
 J. P. Singh & B. K. Roy, The nature of Lyapunov exponents is (+,+,-,-). Is it a hyperchaotic system ?, Chaos, Solitons & Fractals, 92, 73-85, 2016.