Cumulative HXLF of AGN in a volume (V₁₆) defined to contain the bulk of the galaxy population in MQN01, with A_max ∼ 16 cMpc² and Δv_max = ± 1000 km s⁻¹. The red and green lines represent the HXLF estimated for the MQN01 and Spiderweb protoclusters, respectively, centred on the brightest QSOs, CTS G18.01 (ID1) and PSK1138, which are excluded from the analysis. The blue line depicts the HXLF of AGN in the SSA22 protocluster, centred at the location that maximizes the AGN overdensity within V₁₆. The transparent bands indicate the range of values due to Poisson uncertainties. The dashed lines indicate the HXLF of AGN in the field, estimated as in Gilli et al. (2007), with the colours corresponding to the same redshifts as the solid lines for the protoclusters.