Update README.md

README.md

@@ -28,7 +28,7 @@ The constructed BVH will have a layout suitable for construction ('````WALD_32BY
 * ````BVH::WALD_32BYTE```` : A compact format that stores the AABB for a node, along with child pointers and leaf information in a cross-platform-friendly way. The 32-byte size allows for cache-line alignment.
 * ````BVH::VERBOSE```` : A format designed for modifying BVHs, e.g. for post-build optimizations using ````BVH::Optimize()````.
 * ````BVH::AILA_LAINE```` : This format uses 64 bytes per node and stores the AABBs of the two child nodes. This is the format recommended for basic GPU ray tracing.
-* ````BVH::BASIC_BVH4```` : In this format, each node stores four child pointers, reducing the depth of the tree. This improves performance for divergent rays.
+* ````BVH::BASIC_BVH4```` : In this format, each node stores four child pointers, reducing the depth of the tree. This improves performance for divergent rays. Based on the [2008 paper](https://graphics.stanford.edu/~boulos/papers/multi_rt08.pdf) by Ingo Wald et al.
 * ````BVH::BVH4_GPU```` : The ````BASIC_BVH4```` format can be converted to the more compact ````BVH4_GPU```` layout, which will be faster for GPU ray tracing.
 * ````BVH::BASIC_BVH8```` : This format stores eight child pointers, further reducing the depth of the tree. The only purpose is the construction of ````BVH::CWBVH````.
 * ````BVH::CWBVH```` : An advanced 80-byte representation of the 8-wide BVH, for state-of-the-art GPU rendering, based on the [2017 paper](https://research.nvidia.com/publication/2017-07_efficient-incoherent-ray-traversal-gpus-through-compressed-wide-bvhs) by Ylitie et al. and [code by AlanWBFT](https://github.com/AlanIWBFT/CWBVH).