Sketch of a cumulative luminosity distribution. The highly significant bright-end distribution (solid) and its linear extrapolation (dash-dotted) have slope β and are discussed in Sect. 2.3.1. The extension of the bright-end distribution with slope γ (dashed) is discussed in Sect. 2.3.2. The variables on the axes are defined in these two sections. In general the γ-slope can be either flatter than (shown), equal to, or steeper than the β-slope.