diff -r 318b669fe660 -r 9034b44844bd src/Pure/General/graph.scala
--- a/src/Pure/General/graph.scala	Sat Feb 25 13:13:14 2012 +0100
+++ b/src/Pure/General/graph.scala	Sat Feb 25 13:17:38 2012 +0100
@@ -119,7 +119,7 @@
   def is_maximal(x: Key): Boolean = imm_succs(x).isEmpty
 
 
-  /* nodes */
+  /* node operations */
 
   def new_node(x: Key, info: A): Graph[Key, A] =
   {
@@ -152,7 +152,7 @@
     (this /: entries){ case (graph, (x, _)) => if (!pred(x)) graph.del_node(x) else graph }
 
 
-  /* edges */
+  /* edge operations */
 
   def is_edge(x: Key, y: Key): Boolean =
     try { imm_succs(x)(y) }