diff --git a/simple.md b/simple.md
index e421f2216..ec1d27254 100644
--- a/simple.md
+++ b/simple.md
@@ -1,4 +1,5 @@
 # simple
 
-- many [[problems]] we need to solve are actually [[simple]].
+- many [[problems]] we need to solve are actually [[simple]]. they might be hard to solve in the sense of being computationally or otherwise resource-intensive. but their inherent structure is not particularly complex.
+  - [[coordination problems]] are one such subset.