diff --git a/src/client/media/diceCoefficient.png b/src/client/media/diceCoefficient.png
new file mode 100644
index 000000000..5e53906e3
Binary files /dev/null and b/src/client/media/diceCoefficient.png differ
diff --git a/src/client/tree-sitter.js b/src/client/tree-sitter.js
index ab75924ba..03f8dec08 100644
--- a/src/client/tree-sitter.js
+++ b/src/client/tree-sitter.js
@@ -136,16 +136,19 @@ export function isomorphic(node1, node2) {
   return true;
 }
 
+// similarity coefficient
+
+
+/*MD 
+
+![](media/diceCoefficient.png){width=100px}
+MD*/
 export function dice(t1, t2, M) {
   let descendantsT1 = s(t1)
   let descendantsT2 = s(t2)
-
-
   let mappedElements = []
 
   // the ratio of common descendants between two nodes given a set of mappings M
-
-
   for (let m of M) {
     if (descendantsT1.has(m.node1.id) && descendantsT2.has(m.node2.id)) {
       mappedElements.push(m)
@@ -338,7 +341,6 @@ function isLeaf(node) {
 
 
 function lastChanceMatch(mappings, src, dst, maxSize) {
-  debugger
   if (s(src).size < maxSize || s(dst).size < maxSize) {
     let zsMappings = zhangShashaMapping(src, dst,
       function children(node) { return node.children },
@@ -346,16 +348,17 @@ function lastChanceMatch(mappings, src, dst, maxSize) {
       function removeCost() { return 1 },
       function updateCost(from, to) { 
           if (from.type === to.type) {
-            debugger
             return qGramsDifference(label(from), label(from), 2)
           } else {
             return 1
           }
       });
     for (let candidate of zsMappings) {
-      let srcCand = candidate.t1;
-      let dstCand = candidate.t2;
-      addMapping(mappings, srcCand, dstCand);
+      if (candidate.t1  && candidate.t2) {
+        if (!isSrcMapped(candidate.t1, mappings) && !isDstMapped(candidate.t2, mappings)) {
+          addMapping(mappings, candidate.t1, candidate.t2);
+        }
+      }
     }
   }
 }
@@ -371,8 +374,10 @@ function bottomUpPhase(T1, dst, mappings, minDice, maxSize) {
 
   visitPostorder(T1, t => {
     if (!t.parent) {
-      addMapping(mappings, t, dst)
-      lastChanceMatch(mappings, t, dst, maxSize);
+      if (!isSrcMapped(t, mappings)) {
+        addMapping(mappings, t, dst)
+        lastChanceMatch(mappings, t, dst, maxSize);
+      }
     } else if (!isSrcMapped(t, mappings) && !isLeaf(t)) {
       let candidatesList = candidates(t, mappings);
       let best = null;
diff --git a/src/components/tools/lively-container.js b/src/components/tools/lively-container.js
index ac0edfcdb..b08dd0782 100644
--- a/src/components/tools/lively-container.js
+++ b/src/components/tools/lively-container.js
@@ -2932,6 +2932,7 @@ export default class Container extends Morph {
         
         // TEST 
       
+        
         if (unsavedText) {
           // container or editor load text async and we have to interact with them
           // await lively.sleep(1000)
@@ -2940,10 +2941,7 @@ export default class Container extends Morph {
 //           newEditor.textChanged = true
 //           newEditor.lastText = obj.lastText
           newEditor.livelyMigrate(oldEditor)
-          
         }
-       
-        
       })
     } else {
       this.isMigrating = false;
diff --git a/test/tree-sitter-test.js b/test/tree-sitter-test.js
index f89eb7a20..d0e964648 100644
--- a/test/tree-sitter-test.js
+++ b/test/tree-sitter-test.js
@@ -49,6 +49,7 @@ describe('tree-sitter', () => {
         
         expect(matches.length).gt(3)
         
+        debugger
         var result = dice(callExpr1,callExpr2, matches)
         
         expect(result).to.equal(1)
@@ -132,7 +133,7 @@ a   = 3 + 4`])
         expect(matches.length).gt(5)      
         for(let match of matches) {
           if (match.node1.text !== tree1.text) {
-            expect(match.node1.text).to.equal(match.node2.text)            
+            expect(match.node1.text, match.node1.type + " -> " + match.node2.type).to.equal(match.node2.text)            
           }
         }
     })
@@ -175,12 +176,13 @@ if (true) {
       
         // that.tree.language.query("(variable_declarator)@a").captures(this)
         var classDecl1 = tree1.child(0)
-        var classDecl1 = tree2.child(0)
+        var classDecl2 = tree2.child(0)
         
         var matches = match(tree1, tree2)
         
         expect(matches.length).gt(10) 
         
+        debugger
         let found = matches.find(ea => ea.node1.id == classDecl1.id && ea.node2.id == classDecl2.id)
         
         expect(found).to.not.be.undefined