diff --git a/source/net/yacy/kelondro/blob/HeapReader.java b/source/net/yacy/kelondro/blob/HeapReader.java
index 7dbe44dc8..eda2e659e 100644
--- a/source/net/yacy/kelondro/blob/HeapReader.java
+++ b/source/net/yacy/kelondro/blob/HeapReader.java
@@ -42,6 +42,7 @@ import net.yacy.kelondro.io.Writer;
 import net.yacy.kelondro.logging.Log;
 import net.yacy.kelondro.order.ByteOrder;
 import net.yacy.kelondro.order.CloneableIterator;
+import net.yacy.kelondro.order.Digest;
 import net.yacy.kelondro.order.NaturalOrder;
 import net.yacy.kelondro.order.RotateIterator;
 import net.yacy.kelondro.util.FileUtils;
@@ -147,17 +148,17 @@ public class HeapReader {
     private boolean initIndexReadDump() {
         // look for an index dump and read it if it exist
         // if this is successful, return true; otherwise false
-        String fingerprint = HeapWriter.fingerprintFileHash(this.heapFile);
+        String fingerprint = fingerprintFileHash(this.heapFile);
         if (fingerprint == null) {
             Log.logSevere("HeapReader", "cannot generate a fingerprint for " + this.heapFile + ": null");
             return false;
         }
-        File fif = HeapWriter.fingerprintIndexFile(this.heapFile, fingerprint);
+        File fif = fingerprintIndexFile(this.heapFile, fingerprint);
         if (!fif.exists()) fif = new File(fif.getAbsolutePath() + ".gz");
-        File fgf = HeapWriter.fingerprintGapFile(this.heapFile, fingerprint);
+        File fgf = fingerprintGapFile(this.heapFile, fingerprint);
         if (!fgf.exists()) fgf = new File(fgf.getAbsolutePath() + ".gz");
         if (!fif.exists() || !fgf.exists()) {
-            HeapWriter.deleteAllFingerprints(this.heapFile);
+            deleteAllFingerprints(this.heapFile, fif.getName(), fgf.getName());
             return false;
         }
         
@@ -194,6 +195,41 @@ public class HeapReader {
         return !this.index.isEmpty();
     }
     
+    protected static File fingerprintIndexFile(File f, String fingerprint) {
+        assert f != null;
+        return new File(f.getParentFile(), f.getName() + "." + fingerprint + ".idx");
+    }
+    
+    protected static File fingerprintGapFile(File f, String fingerprint) {
+        assert f != null;
+        return new File(f.getParentFile(), f.getName() + "." + fingerprint + ".gap");
+    }
+    
+    protected static String fingerprintFileHash(File f) {
+        assert f != null;
+        assert f.exists() : "file = " + f.toString();
+        String fp = Digest.fastFingerprintB64(f, false);
+        assert fp != null : "file = " + f.toString();
+        if (fp == null) return null;
+        return fp.substring(0, 12);
+    }
+    
+    public static void deleteAllFingerprints(File f, String exception1, String exception2) {
+        File d = f.getParentFile();
+        String n = f.getName();
+        String[] l = d.list();
+        for (int i = 0; i < l.length; i++) {
+            if (!l[i].startsWith(n)) continue;
+            if (exception1 != null && l[i].equals(exception1)) continue;
+            if (exception2 != null && l[i].equals(exception2)) continue;
+            if (l[i].endsWith(".idx") ||
+                l[i].endsWith(".gap") ||
+                l[i].endsWith(".idx.gz") ||
+                l[i].endsWith(".gap.gz")
+               ) FileUtils.deletedelete(new File(d, l[i]));
+        }
+    }
+    
     private void initIndexReadFromHeap() throws IOException {
         // this initializes the this.index object by reading positions from the heap file
         Log.logInfo("HeapReader", "generating index for " + heapFile.toString() + ", " + (file.length() / 1024 / 1024) + " MB. Please wait.");
@@ -513,16 +549,16 @@ public class HeapReader {
                 // to speed up the next start
                 try {
                     long start = System.currentTimeMillis();
-                    String fingerprint = HeapWriter.fingerprintFileHash(this.heapFile);
+                    String fingerprint = fingerprintFileHash(this.heapFile);
                     if (fingerprint == null) {
                         Log.logSevere("kelondroBLOBHeap", "cannot write a dump for " + heapFile.getName()+ ": fingerprint is null");
                     } else {
-                        free.dump(HeapWriter.fingerprintGapFile(this.heapFile, fingerprint));
+                        free.dump(fingerprintGapFile(this.heapFile, fingerprint));
                     }
                     free.clear();
                     free = null;
                     if (fingerprint != null) {
-                        index.dump(HeapWriter.fingerprintIndexFile(this.heapFile, fingerprint));
+                        index.dump(fingerprintIndexFile(this.heapFile, fingerprint));
                         Log.logInfo("kelondroBLOBHeap", "wrote a dump for the " + this.index.size() +  " index entries of " + heapFile.getName()+ " in " + (System.currentTimeMillis() - start) + " milliseconds.");
                     }
                     index.close();
diff --git a/source/net/yacy/kelondro/blob/HeapWriter.java b/source/net/yacy/kelondro/blob/HeapWriter.java
index 9d1ad632c..ef6aa756a 100644
--- a/source/net/yacy/kelondro/blob/HeapWriter.java
+++ b/source/net/yacy/kelondro/blob/HeapWriter.java
@@ -34,7 +34,6 @@ import net.yacy.kelondro.index.HandleMap;
 import net.yacy.kelondro.index.RowSpaceExceededException;
 import net.yacy.kelondro.logging.Log;
 import net.yacy.kelondro.order.ByteOrder;
-import net.yacy.kelondro.order.Digest;
 import net.yacy.kelondro.util.FileUtils;
 
 
@@ -110,34 +109,6 @@ public final class HeapWriter {
         //os.flush(); // necessary? may cause bad IO performance :-(
     }
     
-    protected static File fingerprintIndexFile(File f, String fingerprint) {
-        assert f != null;
-        return new File(f.getParentFile(), f.getName() + "." + fingerprint + ".idx");
-    }
-    
-    protected static File fingerprintGapFile(File f, String fingerprint) {
-        assert f != null;
-        return new File(f.getParentFile(), f.getName() + "." + fingerprint + ".gap");
-    }
-    
-    protected static String fingerprintFileHash(File f) {
-        assert f != null;
-        assert f.exists() : "file = " + f.toString();
-        String fp = Digest.fastFingerprintB64(f, false);
-        assert fp != null : "file = " + f.toString();
-        if (fp == null) return null;
-        return fp.substring(0, 12);
-    }
-    
-    public static void deleteAllFingerprints(File f) {
-        File d = f.getParentFile();
-        String n = f.getName();
-        String[] l = d.list();
-        for (int i = 0; i < l.length; i++) {
-            if (l[i].startsWith(n) && (l[i].endsWith(".idx") || l[i].endsWith(".gap") || l[i].endsWith(".idx.gz") || l[i].endsWith(".gap.gz"))) FileUtils.deletedelete(new File(d, l[i]));
-        }
-    }
-    
     /**
      * close the BLOB table
      * @throws  
@@ -160,12 +131,12 @@ public final class HeapWriter {
             // now we can create a dump of the index and the gap information
             // to speed up the next start
             long start = System.currentTimeMillis();
-            String fingerprint = HeapWriter.fingerprintFileHash(this.heapFileREADY);
+            String fingerprint = HeapReader.fingerprintFileHash(this.heapFileREADY);
             if (fingerprint == null) {
                 Log.logSevere("kelondroBLOBHeapWriter", "cannot write a dump for " + heapFileREADY.getName()+ ": fingerprint is null");
             } else {
-                new Gap().dump(fingerprintGapFile(this.heapFileREADY, fingerprint));
-                index.dump(fingerprintIndexFile(this.heapFileREADY, fingerprint));
+                new Gap().dump(HeapReader.fingerprintGapFile(this.heapFileREADY, fingerprint));
+                index.dump(HeapReader.fingerprintIndexFile(this.heapFileREADY, fingerprint));
                 Log.logInfo("kelondroBLOBHeapWriter", "wrote a dump for the " + this.index.size() +  " index entries of " + heapFileREADY.getName()+ " in " + (System.currentTimeMillis() - start) + " milliseconds.");
             }
             index.close();
diff --git a/source/net/yacy/kelondro/data/citation/CitationReferenceRow.java b/source/net/yacy/kelondro/data/citation/CitationReferenceRow.java
index 52a8a6814..31b97c9d9 100644
--- a/source/net/yacy/kelondro/data/citation/CitationReferenceRow.java
+++ b/source/net/yacy/kelondro/data/citation/CitationReferenceRow.java
@@ -26,6 +26,8 @@
 
 package net.yacy.kelondro.data.citation;
 
+import java.util.Collection;
+
 import net.yacy.kelondro.data.word.Word;
 import net.yacy.kelondro.index.Column;
 import net.yacy.kelondro.index.Row;
@@ -214,7 +216,7 @@ public final class CitationReferenceRow implements Reference /*, Cloneable*/ {
         throw new UnsupportedOperationException();
     }
 
-    public int positions() {
+    public Collection<Integer> positions() {
         throw new UnsupportedOperationException();
     }
 
diff --git a/source/net/yacy/kelondro/data/image/ImageReferenceRow.java b/source/net/yacy/kelondro/data/image/ImageReferenceRow.java
index c3922da5e..a8b3e4e17 100644
--- a/source/net/yacy/kelondro/data/image/ImageReferenceRow.java
+++ b/source/net/yacy/kelondro/data/image/ImageReferenceRow.java
@@ -26,6 +26,9 @@
 
 package net.yacy.kelondro.data.image;
 
+import java.util.ArrayList;
+import java.util.Collection;
+
 import net.yacy.kelondro.data.word.Word;
 import net.yacy.kelondro.index.Column;
 import net.yacy.kelondro.index.Row;
@@ -226,8 +229,8 @@ public final class ImageReferenceRow extends AbstractReference implements /*Imag
         return (int) this.entry.getColLong(col_hitcount);
     }
 
-    public int positions() {
-        return 1;
+    public Collection<Integer> positions() {
+        return new ArrayList<Integer>(0);
     }
 
     public int position(int p) {
diff --git a/source/net/yacy/kelondro/data/image/ImageReferenceVars.java b/source/net/yacy/kelondro/data/image/ImageReferenceVars.java
index 0e4e46357..90a6c7758 100644
--- a/source/net/yacy/kelondro/data/image/ImageReferenceVars.java
+++ b/source/net/yacy/kelondro/data/image/ImageReferenceVars.java
@@ -26,7 +26,8 @@
 
 package net.yacy.kelondro.data.image;
 
-import java.util.ArrayList;
+import java.util.Collection;
+import java.util.concurrent.ConcurrentLinkedQueue;
 
 import net.yacy.kelondro.index.Row.Entry;
 import net.yacy.kelondro.order.Bitfield;
@@ -53,7 +54,7 @@ public class ImageReferenceVars extends AbstractReference implements ImageRefere
                posinphrase, posofphrase,
                urlcomps, urllength, virtualAge,
                wordsintext, wordsintitle;
-    private final ArrayList<Integer> positions;
+    private final ConcurrentLinkedQueue<Integer> positions;
     public double termFrequency;
     
     public ImageReferenceVars(
@@ -64,7 +65,7 @@ public class ImageReferenceVars extends AbstractReference implements ImageRefere
             final int      hitcount,      // how often appears this word in the text
             final int      wordcount,     // total number of words
             final int      phrasecount,   // total number of phrases
-            final ArrayList<Integer> ps,  // positions of words that are joined into the reference
+            final ConcurrentLinkedQueue<Integer> ps,  // positions of words that are joined into the reference
             final int      posinphrase,   // position of word in its phrase
             final int      posofphrase,   // number of the phrase where word appears
             final long     lastmodified,  // last-modified time of the document where word appears
@@ -89,8 +90,8 @@ public class ImageReferenceVars extends AbstractReference implements ImageRefere
         this.llocal = outlinksSame;
         this.lother = outlinksOther;
         this.phrasesintext = phrasecount;
-        this.positions = new ArrayList<Integer>(ps.size());
-        for (int i = 0; i < ps.size(); i++) this.positions.add(ps.get(i));
+        this.positions = new ConcurrentLinkedQueue<Integer>();
+        for (Integer i: ps) this.positions.add(i);
         this.posinphrase = posinphrase;
         this.posofphrase = posofphrase;
         this.urlcomps = urlComps;
@@ -112,8 +113,8 @@ public class ImageReferenceVars extends AbstractReference implements ImageRefere
         this.llocal = e.llocal();
         this.lother = e.lother();
         this.phrasesintext = e.phrasesintext();
-        this.positions = new ArrayList<Integer>(e.positions());
-        for (int i = 0; i < e.positions(); i++) this.positions.add(e.position(i));
+        this.positions = new ConcurrentLinkedQueue<Integer>();
+        for (Integer i: e.positions()) this.positions.add(i);
         this.posinphrase = e.posinphrase();
         this.posofphrase = e.posofphrase();
         this.urlcomps = e.urlcomps();
@@ -227,12 +228,8 @@ public class ImageReferenceVars extends AbstractReference implements ImageRefere
         return posinphrase;
     }
 
-    public int positions() {
-        return this.positions.size();
-    }
-
-    public int position(int p) {
-        return this.positions.get(p);
+    public Collection<Integer> positions() {
+        return this.positions;
     }
 
     public int posofphrase() {
@@ -248,7 +245,7 @@ public class ImageReferenceVars extends AbstractReference implements ImageRefere
                 hitcount,      // how often appears this word in the text
                 wordsintext,   // total number of words
                 phrasesintext, // total number of phrases
-                positions.get(0), // position of word in all words
+                positions.iterator().next(), // position of word in all words
                 posinphrase,   // position of word in its phrase
                 posofphrase,   // number of the phrase where word appears
                 lastModified,  // last-modified time of the document where word appears
@@ -347,7 +344,7 @@ public class ImageReferenceVars extends AbstractReference implements ImageRefere
         
         // combine the distance
         ImageReference oe = (ImageReference) r; 
-        for (int i = 0; i < r.positions(); i++) this.positions.add(r.position(i));
+        for (Integer i: r.positions()) this.positions.add(i);
         this.posinphrase = (this.posofphrase == oe.posofphrase()) ? Math.min(this.posinphrase, oe.posinphrase()) : 0;
         this.posofphrase = Math.min(this.posofphrase, oe.posofphrase());
 
diff --git a/source/net/yacy/kelondro/data/navigation/NavigationReferenceRow.java b/source/net/yacy/kelondro/data/navigation/NavigationReferenceRow.java
index ae2c3cda0..f26f5dd8d 100644
--- a/source/net/yacy/kelondro/data/navigation/NavigationReferenceRow.java
+++ b/source/net/yacy/kelondro/data/navigation/NavigationReferenceRow.java
@@ -26,6 +26,8 @@
 
 package net.yacy.kelondro.data.navigation;
 
+import java.util.Collection;
+
 import net.yacy.kelondro.data.word.Word;
 import net.yacy.kelondro.index.Column;
 import net.yacy.kelondro.index.Row;
@@ -174,7 +176,7 @@ public final class NavigationReferenceRow extends AbstractReference implements N
         throw new UnsupportedOperationException();
     }
 
-    public int positions() {
+    public Collection<Integer> positions() {
         throw new UnsupportedOperationException();
     }
     
diff --git a/source/net/yacy/kelondro/data/navigation/NavigationReferenceVars.java b/source/net/yacy/kelondro/data/navigation/NavigationReferenceVars.java
index fd6f92b78..794c9607f 100644
--- a/source/net/yacy/kelondro/data/navigation/NavigationReferenceVars.java
+++ b/source/net/yacy/kelondro/data/navigation/NavigationReferenceVars.java
@@ -26,6 +26,8 @@
 
 package net.yacy.kelondro.data.navigation;
 
+import java.util.Collection;
+
 import net.yacy.kelondro.index.Row.Entry;
 import net.yacy.kelondro.rwi.AbstractReference;
 import net.yacy.kelondro.rwi.Reference;
@@ -146,7 +148,7 @@ public class NavigationReferenceVars  extends AbstractReference implements Navig
         throw new UnsupportedOperationException();
     }
 
-    public int positions() {
+    public Collection<Integer> positions() {
         throw new UnsupportedOperationException();
     }
     
diff --git a/source/net/yacy/kelondro/data/word/WordReferenceRow.java b/source/net/yacy/kelondro/data/word/WordReferenceRow.java
index 873632857..17cd59aea 100644
--- a/source/net/yacy/kelondro/data/word/WordReferenceRow.java
+++ b/source/net/yacy/kelondro/data/word/WordReferenceRow.java
@@ -26,6 +26,9 @@
 
 package net.yacy.kelondro.data.word;
 
+import java.util.ArrayList;
+import java.util.Collection;
+
 import net.yacy.kelondro.index.Column;
 import net.yacy.kelondro.index.Row;
 import net.yacy.kelondro.index.Row.Entry;
@@ -257,8 +260,8 @@ public final class WordReferenceRow extends AbstractReference implements WordRef
         return (int) this.entry.getColLong(col_hitcount);
     }
 
-    public int positions() {
-        return 1;
+    public Collection<Integer> positions() {
+        return new ArrayList<Integer>(0);
     }
 
     public int position(final int p) {
diff --git a/source/net/yacy/kelondro/data/word/WordReferenceVars.java b/source/net/yacy/kelondro/data/word/WordReferenceVars.java
index ffab3d7c8..a7a7f55f1 100644
--- a/source/net/yacy/kelondro/data/word/WordReferenceVars.java
+++ b/source/net/yacy/kelondro/data/word/WordReferenceVars.java
@@ -26,11 +26,10 @@
 
 package net.yacy.kelondro.data.word;
 
-import java.util.ArrayList;
-import java.util.Collections;
+import java.util.Collection;
 import java.util.Comparator;
-import java.util.List;
 import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.Semaphore;
 
@@ -62,7 +61,7 @@ public class WordReferenceVars extends AbstractReference implements WordReferenc
                posinphrase, posofphrase,
                urlcomps, urllength, virtualAge,
                wordsintext, wordsintitle;
-    private final List<Integer> positions;
+    private final ConcurrentLinkedQueue<Integer> positions;
     public double termFrequency;
     
     public WordReferenceVars(
@@ -73,7 +72,7 @@ public class WordReferenceVars extends AbstractReference implements WordReferenc
             final int      hitcount,      // how often appears this word in the text
             final int      wordcount,     // total number of words
             final int      phrasecount,   // total number of phrases
-            final List<Integer> ps,       // positions of words that are joined into the reference
+            final ConcurrentLinkedQueue<Integer> ps,       // positions of words that are joined into the reference
             final int      posinphrase,   // position of word in its phrase
             final int      posofphrase,   // number of the phrase where word appears
             final long     lastmodified,  // last-modified time of the document where word appears
@@ -98,8 +97,8 @@ public class WordReferenceVars extends AbstractReference implements WordReferenc
         this.llocal = outlinksSame;
         this.lother = outlinksOther;
         this.phrasesintext = phrasecount;
-        this.positions = Collections.synchronizedList(new ArrayList<Integer>(ps.size()));
-        for (int i = 0; i < ps.size(); i++) this.positions.add(ps.get(i));
+        this.positions = new ConcurrentLinkedQueue<Integer>();
+        for (Integer i: ps) this.positions.add(i);
         this.posinphrase = posinphrase;
         this.posofphrase = posofphrase;
         this.urlcomps = urlComps;
@@ -121,8 +120,8 @@ public class WordReferenceVars extends AbstractReference implements WordReferenc
         this.llocal = e.llocal();
         this.lother = e.lother();
         this.phrasesintext = e.phrasesintext();
-        this.positions = new ArrayList<Integer>(e.positions());
-        for (int i = 0; i < e.positions(); i++) this.positions.add(e.position(i));
+        this.positions = new ConcurrentLinkedQueue<Integer>();
+        for (Integer i: e.positions()) this.positions.add(i);
         this.posinphrase = e.posinphrase();
         this.posofphrase = e.posofphrase();
         this.urlcomps = e.urlcomps();
@@ -237,14 +236,10 @@ public class WordReferenceVars extends AbstractReference implements WordReferenc
         return posinphrase;
     }
 
-    public int positions() {
-        return this.positions.size();
+    public Collection<Integer> positions() {
+        return this.positions;
     }
-
-    public int position(final int p) {
-        return this.positions.get(p);
-    }
-
+    
     public int posofphrase() {
         return posofphrase;
     }
@@ -258,7 +253,7 @@ public class WordReferenceVars extends AbstractReference implements WordReferenc
                 hitcount,      // how often appears this word in the text
                 wordsintext,   // total number of words
                 phrasesintext, // total number of phrases
-                positions.get(0), // position of word in all words
+                positions.size() == 0 ? 1 : positions.iterator().next(), // position of word in all words
                 posinphrase,   // position of word in its phrase
                 posofphrase,   // number of the phrase where word appears
                 lastModified,  // last-modified time of the document where word appears
@@ -357,7 +352,7 @@ public class WordReferenceVars extends AbstractReference implements WordReferenc
         
         // combine the distance
         WordReference oe = (WordReference) r; 
-        for (int i = 0; i < r.positions(); i++) this.positions.add(r.position(i));
+        for (Integer i: r.positions()) this.positions.add(i);
         this.posinphrase = (this.posofphrase == oe.posofphrase()) ? Math.min(this.posinphrase, oe.posinphrase()) : 0;
         this.posofphrase = Math.min(this.posofphrase, oe.posofphrase());
 
diff --git a/source/net/yacy/kelondro/rwi/AbstractReference.java b/source/net/yacy/kelondro/rwi/AbstractReference.java
index cffb7fbfd..0429e0821 100644
--- a/source/net/yacy/kelondro/rwi/AbstractReference.java
+++ b/source/net/yacy/kelondro/rwi/AbstractReference.java
@@ -26,26 +26,27 @@
 
 package net.yacy.kelondro.rwi;
 
-import java.util.List;
+import java.util.Collection;
+import java.util.Iterator;
 
 
 public abstract class AbstractReference implements Reference {
 
-    protected static void a(List<Integer> a, int i) {
+    protected static void a(Collection<Integer> a, int i) {
         assert a != null;
         if (i < 0) return; // signal for 'do nothing'
-        synchronized (a) {
-            a.clear();
-            a.add(i);
-        }
+        a.clear();
+        a.add(i);
     }
-    protected static int max(List<Integer> a, List<Integer> b) {
+    
+    protected static int max(Collection<Integer> a, Collection<Integer> b) {
         assert a != null;
         if (a.size() == 0) return max(b);
         if (b.size() == 0) return max(a);
         return Math.max(max(a), max(b));
     }
-    protected static int min(List<Integer> a, List<Integer> b) {
+    
+    protected static int min(Collection<Integer> a, Collection<Integer> b) {
         assert a != null;
         if (a.size() == 0) return min(b);
         if (b.size() == 0) return min(a);
@@ -56,46 +57,56 @@ public abstract class AbstractReference implements Reference {
         return Math.min(ma, mb);
     }
 
-    private static int max(List<Integer> a) {
+    private static int max(Collection<Integer> a) {
         assert a != null;
         if (a.size() == 0) return -1;
-        if (a.size() == 1) return a.get(0);
-        if (a.size() == 2) return Math.max(a.get(0), a.get(1));
-        int r = a.get(0);
-        for (int i = 1; i < a.size(); i++) if (a.get(i) > r) r = a.get(i);
+        Iterator<Integer> i = a.iterator();
+        if (a.size() == 1) return i.next();
+        if (a.size() == 2) return Math.max(i.next(), i.next());
+        int r = i.next();
+        int s;
+        while (i.hasNext()) {
+            s = i.next();
+            if (s > r) r = s;
+        }
         return r;
     }
-    private static int min(List<Integer> a) {
+    
+    private static int min(Collection<Integer> a) {
         assert a != null;
         if (a.size() == 0) return -1;
-        if (a.size() == 1) return a.get(0);
-        if (a.size() == 2) return Math.min(a.get(0), a.get(1));
-        int r = a.get(0);
-        for (int i = 1; i < a.size(); i++) if (a.get(i) < r) r = a.get(i);
+        Iterator<Integer> i = a.iterator();
+        if (a.size() == 1) return i.next();
+        if (a.size() == 2) return Math.min(i.next(), i.next());
+        int r = i.next();
+        int s;
+        while (i.hasNext()) {
+            s = i.next();
+            if (s <r) r = s;
+        }
         return r;
     }
     
     public int maxposition() {
-        assert positions() > 0;
-        if (positions() == 1) return position(0);
-        int p = position(0);
-        for (int i = positions() - 1; i > 0; i--) if (position(i) > p) p = position(i);
-        return p;
+        assert positions().size() > 0;
+        return max(positions());
     }
     
     public int minposition() {
-        assert positions() > 0;
-        if (positions() == 1) return position(0);
-        int p = position(0);
-        for (int i = positions() - 1; i > 0; i--) if (position(i) < p) p = position(i);
-        return p;
+        assert positions().size() > 0;
+        return min(positions());
     }
     
     public int distance() {
+        if (positions().size() < 2) return 0;
         int d = 0;
-        for (int i = 0; i < this.positions() - 1; i++) {
-            d += Math.abs(this.position(i) - this.position(i + 1));
+        Iterator<Integer> i = positions().iterator();
+        int s0 = i.next(), s1;
+        while (i.hasNext()) {
+            s1 = i.next();
+            d += Math.abs(s0 - s1);
+            s0 = s1;
         }
-        return d;
+        return d / (positions().size() - 1);
     }
 }
diff --git a/source/net/yacy/kelondro/rwi/Reference.java b/source/net/yacy/kelondro/rwi/Reference.java
index 2edb445ca..bf41f4c92 100644
--- a/source/net/yacy/kelondro/rwi/Reference.java
+++ b/source/net/yacy/kelondro/rwi/Reference.java
@@ -26,6 +26,8 @@
 
 package net.yacy.kelondro.rwi;
 
+import java.util.Collection;
+
 import net.yacy.kelondro.index.Row.Entry;
 
 public interface Reference {
@@ -48,14 +50,12 @@ public interface Reference {
 
     public void join(final Reference oe);
     
-    public int positions();
+    public Collection<Integer> positions();
     
     public int maxposition();
     
     public int minposition();
     
-    public int position(int p);
-    
     public int distance();
         
 }