--- a/Interval.st	Thu Jun 25 06:36:01 2015 +0200
+++ b/Interval.st	Fri Jun 26 06:36:52 2015 +0200
@@ -1,3 +1,5 @@
+"{ Encoding: utf8 }"
+
 "
  COPYRIGHT (c) 1989 by Claus Gittinger
               All Rights Reserved
@@ -11,6 +13,8 @@
 "
 "{ Package: 'stx:libbasic' }"
 
+"{ NameSpace: Smalltalk }"
+
 ReadOnlySequenceableCollection subclass:#Interval
 	instanceVariableNames:'start stop step'
 	classVariableNames:''
@@ -44,6 +48,10 @@
     For example, the interval (1 to:5) containes the elements (1 2 3 4 5) and
     (1 to:6 by:2) contains (1 3 5).
 
+    The step may be negative, to count backward:
+    (5 to:1 by:-1) contains (5 4 3 2 1), and (6 to:1 by:-2) contains (6 4 2).
+
+
     examples:
 
         (1 to:10) do:[:i | Transcript showCR:i]
@@ -535,12 +543,12 @@
         (start < stop) ifTrue:[
             ^ 0
         ].
-        ^ stop - start // step + 1
+        ^ (start - stop) // step abs + 1
     ].
     (stop < start) ifTrue:[
         ^ 0
     ].
-    ^ stop - start // step + 1
+    ^ (stop - start) // step + 1
 ! !
 
 !Interval methodsFor:'set operations'!
@@ -690,10 +698,10 @@
 !Interval class methodsFor:'documentation'!
 
 version
-    ^ '$Header: /cvs/stx/stx/libbasic/Interval.st,v 1.57 2014-07-10 12:23:57 cg Exp $'
+    ^ '$Header$'
 !
 
 version_CVS
-    ^ '$Header: /cvs/stx/stx/libbasic/Interval.st,v 1.57 2014-07-10 12:23:57 cg Exp $'
+    ^ '$Header$'
 ! !