diff --git a/best.c b/best.c
index d781f42..c8a82c7 100644
--- a/best.c
+++ b/best.c
@@ -61,14 +61,28 @@ int check_best(res, nops, node, values, ops)
         nbests=0;
         found=1;
         //return 1;
-    } /*else if (diff == bestdiff && nops == bestops) {
-#       ifdef DEBUG_BEST
-        printf("NEW BEST SOLUTION (%d):  res=%d diff=%d nops=%d\n", nbests+1, res, diff, nops);
-        print_node(node, TREE_TOP, 0, 0);
-#       endif
+    } else if (diff == bestdiff && nops == bestops) {
+        // if (nbests) {
         found=2;
-        }*/
-    if (found==1) {
+        for (i=0; i<nbests; ++i) {
+            if (compare_nodes(node, bests[i].root, 0)) {
+                found=0;
+                break;
+            }
+        }
+#       ifdef DEBUG_BEST
+        if (found==2) {
+            printf("new diff solution (%d): res=%d diff=%d nops=%d\n",
+                   nbests+1, res, diff, nops);
+            print_node(node, TREE_TOP, 0, 0);
+        } else {
+            printf("skipping duplicate solution (%d): res=%d diff=%d nops=%d\n",
+                   nbests+1, res, diff, nops);
+        }
+#       endif
+    }
+    //}
+    if (found) {
         set_timer(&(bests[nbests].timer));
         bests[nbests].res=res;
         bests[nbests].diff=diff;
diff --git a/lceb.h b/lceb.h
index bbb060e..d1e5fa6 100644
--- a/lceb.h
+++ b/lceb.h
@@ -68,6 +68,7 @@ typedef struct best {
 /* tree.c */
 extern NODE *get_node();
 extern void free_node(NODE *node);
+extern int compare_nodes(NODE *node1, NODE *node2, int depth);
 extern void print_node(NODE *node, char side, int depth, int details);
 extern void print_tree(TREE *tree, int details);
 extern void print_trees(int details);
diff --git a/tree.c b/tree.c
index e30ae18..fe66629 100644
--- a/tree.c
+++ b/tree.c
@@ -54,6 +54,49 @@ void free_node(node)
     freenodes=node;
 }
 
+int compare_nodes(node1, node2, depth)
+    NODE *node1, *node2;
+    int depth;
+{
+    int equal=0;
+
+    // we must also consider the case n1->left == n2->right, and vice-et-versa.
+#   ifdef DEBUG_TREE
+    if (depth==0) {
+        printf("compare trees: [ ");
+        print_node(node1, TREE_TOP, 0, 4);
+        printf(" ] and [ ");
+        print_node(node2, TREE_TOP, 0, 4);
+        printf(" ] ");
+    }
+#   endif
+    if (node1->type==node2->type) {
+        switch (node1->type) {
+            case TREE_LEAF:
+                if (node1->val==node2->val)
+                    equal=1;
+                break;
+            case TREE_NODE:
+                if (node1->op == node2->op) {
+                    if (compare_nodes(node1->left, node2->left, depth+1) &&
+                        compare_nodes(node1->right, node2->right, depth+1)) {
+                        equal=1;
+                    } else if (compare_nodes(node1->left, node2->right, depth+1) &&
+                               compare_nodes(node1->right, node2->left, depth+1)) {
+                        equal=1;
+                    }
+                }
+                break;
+        }
+    }
+#   ifdef DEBUG_TREE
+    if (depth==0) {
+        printf(" = %d\n", equal);
+    }
+#   endif
+    return equal;
+}
+
 void print_node(node, side, depth, details)
     NODE *node;
     char side;
@@ -120,7 +163,7 @@ void print_node(node, side, depth, details)
                 printf(")");
             }
             break;
-        case 2:
+        case 2:                                   /* tree */
             /* left padding */
             for (i=0; i<=depth; ++i)
                 printf("  ");
@@ -181,6 +224,7 @@ TREE *new_tree(name)
     return tree;
 }
 
+
 NODE *dup_node(src)
     NODE *src;
 {
@@ -269,14 +313,14 @@ void gen_reduced_trees(n)
     };
     char *seq4[]= {
         "101010100",
-        "110010100",
-        "101100100"
+        "101100100",
+        "110010100"
     };
     char *seq5[]= {
         "10101010100",
-        "11001010100",
-        "10110010100",
         "10101100100",
+        "10110010100",
+        "11001010100",
         "11001100100",
         "11010010100"
     };