diff --git a/docs/notes_120_cell.md b/docs/notes_120_cell.md
index afec8b2..1022d42 100644
--- a/docs/notes_120_cell.md
+++ b/docs/notes_120_cell.md
@@ -182,3 +182,7 @@ do the rest by hand
 113 37 53 93
 
 
+Another idea - look at colouring the vertices of a dodecahedron according to
+the four compound tetrahedra and see if this can be repeated automatically to
+neighbouring cells
+