Figures 1 through 4

Fig. 1: β2 = 0.3; β4 = 0b, 0.15r, -0.15g

Fig. 2: β2 = 0.6; β4 = 0b, 0.15r, -0.15g

Fig. 3: β2 = -0.3; β4 = 0b, 0.15r, -0.15g

Fig. 4: β2 = -0.6; β4 = 0b, 0.15r, -0.15g
Notation: In the above figures β4 = 0b, 0.15r, -0.15g indicates that the black line corresponds to β4 = 0, the red line to &beta4 = 0.15, and the green line to β4 = -0.15 .