Larry Aupperle and Pat Hanrahan. Proceedings of SIGGRAPH 1993
We have implemented and analyzed this algorithm over surfaces exhibiting glossy specular and diffuse reflection. Theoretical growth in light transport interactions is shown to be $O(n \log n)$ for sufficient refinement, where $n$ is the number of elements at the finest level of subdivision within the environment --- in trials, this growth has been nearly linear. Naive implementation of three point transport would require $O(n^3)$ element-triple interactions.