so I am not new to interactive graphics programming, but I wanted to try out advanced techniques. Currently I am struggling to understand how the author of the 2011 paper "Interactive Indirect Illumination Using Voxel Cone Tracing" (Crassin et al) manages to solve the rendering equation. Specifically in section 6 he claims that the hemisphere can be partitioned into a sum of integrals. I know about the Riemann sum, but this doesn't look like it. So my question: How does cone tracing as explained in the paper solve the rendering equation?