diff --git a/rs.rkt b/rs.rkt
index 2c07a6d..3bd66e3 100644
--- a/rs.rkt
+++ b/rs.rkt
@@ -139,7 +139,8 @@
 
 ;;; A state of a reaction system is a set of species representing the
 ;;; result of the application of the reactions from the previous
-;;; steps, plus the rest of the context sequence.
+;;; steps, plus the rest of the context sequence.  When the context
+;;; sequence is empty, nothing is added to the current state.
 (struct state (result rest-contexts) #:transparent)
 
 ;;; The dynamics of the reaction system only stores the reaction