diff --git a/ref/vk/TODO.md b/ref/vk/TODO.md
index 4dabb5b0dc..da9b5d8c92 100644
--- a/ref/vk/TODO.md
+++ b/ref/vk/TODO.md
@@ -4,6 +4,7 @@
     - [ ] alpha^2 == 0 ???
     - [ ] various N,L,V collinearities, zero denoms and infinities
         - [ ] h_dot_l | h_dot_v < .0 because of numerical precision
+        - [ ] ggxV|ggxG denoms->0
 
 # 2024-01-08 E359
 - [-] find and fix MORE NaNs