Cumulative contribution (multiplied by the energy ﹩E_{0}﹩) to the predicted CXB at ﹩E_{0}=30﹩ keV, yielded by sources at progressively larger redshifts. The solid line shows the total CXB produced by sources with all luminosities. The other lines show the contributions of AGNs with luminosities L_X (in units of ergs s⁻¹, in the band 2–10 keV) in the ranges ﹩42< \mathrm{log}\,L_{\mathrm{X}\,}< 43.5﹩ (dotted line), ﹩43.5< \mathrm{log}\,L_{\mathrm{X}\,}< 44.5﹩ (dot‐dashed line), and ﹩44.5< \mathrm{log}\,L_{\mathrm{X}\,}﹩ (long‐dashed line). The shaded strip is the value 43 keV cm﹩^{-2}﹩ s﹩^{-1}﹩ sr﹩^{-1}﹩ measured by HEAO 1 A‐2 (Gruber et al. 1999).