Evolution of the and parameters with redshift. Orange points (along with their uncertainties) are the results of the fitting procedure of the function in narrow redshift bins (see Sect. 3 for details). The red solid line represents the predicted value of 4/7 (Sect. 4). The blue solid line and shaded area represent the and from the global fit using luminosities as discussed in Sect. 3. The grey solid and dashed lines are the weighted means with uncertainties of the orange points.