diff --git a/src/set/base.c b/src/set/base.c
index 0b93fbb..141801a 100644
--- a/src/set/base.c
+++ b/src/set/base.c
@@ -4,36 +4,6 @@
 #include "../../include/set.h"
 #include "../__internal/rbtree.h"
 
-/*#####################################################################################################################*/
-
-
-static int tree_compare(rbiter_t* s0, rbiter_t* s1, vtype t) {
-    rbnode_t* p0;
-    rbnode_t* p1;
-    int      cmp;
-
-    for(;;) {
-        p0 = rbiter_next(s0);
-        p1 = rbiter_next(s1);
-
-        if (rbnode_is_empty(p0) || rbnode_is_empty(p1)) {
-            goto end_;
-        } else cmp = vnode_compare(&p0->value, t, &p1->value, t);
-
-        if (cmp != 0) break;
-    }
-
-    for(;;) {
-        p0 = rbiter_next(s0);
-        p1 = rbiter_next(s1);
-
-        if (rbnode_is_empty(p0) || rbnode_is_empty(p1)) {
-          end_:
-            if (p0 == p1) return cmp;
-            return (rbnode_is_empty(p0)) ? -1 : 1;
-        }
-    }
-}
 
 /*#####################################################################################################################*/
 
@@ -43,10 +13,13 @@ void vset_init(vtype_set* x, vtype t) {
     x->type = t;
 }
 
+
 void vset_free(vtype_set* x) {
     rbnode_t* t;
     rbnode_t* c;
 
+    c = x->root;
+
     while (!rbnode_is_empty(x->root)) {
         if (!rbnode_is_empty(c->left)) {
             c = c->left;
@@ -71,28 +44,61 @@ void vset_free(vtype_set* x) {
     x->type = 0;
 }
 
+
 size_t vset_size(const vtype_set* x) {
-    size_t   n;
-    rbiter_t i;
+    stack_t   s = { .prev = 0, .value = x->root };
+    size_t    n = 0;
+    rbnode_t* c;
 
-    n = 0;
-
-    if (rbiter_init(&i, &x->root, 0)) {
-        while (!rbnode_is_empty(rbiter_next(&i)))
-            ++n;
+    while ((c = stack_pop(&s))) {
+        ++n;
+        if (!rbnode_is_empty(c->left))
+            stack_push(&s, c->left);
+        if (!rbnode_is_empty(c->right))
+            stack_push(&s, c->right);
     }
 
     return n;
 }
 
+
 int vset_compare(const vtype_set* s0, const vtype_set* s1) {
-    rbiter_t iter[2];
+    stack_t s = { .prev = 0, .value = 0 };
+    vtype   t = s0->type;
+    int     c = 0;
 
-    if (s0 == s1) return 0;
-    if (s0->type == s1->type) {
-        rbiter_init(iter+0, &s0->root, RBI_INORDER);
-        rbiter_init(iter+1, &s1->root, RBI_INORDER);
+    if (s0 == s1 || s0->root == s1->root) return 0;
+    if (s0->type != s1->type) return s0->type - s1->type;
 
-        return tree_compare(iter+0, iter+1, s0->type);
-    } else return s0->type < s1->type ? -1 : 1;
+    stack_push(&s, s0->root);
+    stack_push(&s, s1->root);
+
+    for (rbnode_t *c0, *c1;;) {
+        c0 = stack_pop(&s);
+        c1 = stack_pop(&s);
+
+        if (is_null(c0)) return 0;
+
+        if (rbnode_is_empty(c0) || rbnode_is_empty(c1)) {
+            if (c0 != c1) {
+                stack_flush(&s);
+                return rbnode_is_empty(c0) ? -1 : 1;
+            }
+        } else if ((c = vnode_compare(c0->value, t, c1->value, t))) {
+            if (c0->left == c1->right) {
+                c = vnode_compare(c1->value, t, c0->right->value, t);
+                if (!c) c = vnode_compare(c1->left->value, t, c0->value, t);
+            } else if (c0->right == c1->left) {
+                c = vnode_compare(c0->value, t, c1->right->value, t);
+                if (!c) c = vnode_compare(c0->left->value, t, c1->value, t);
+            }
+
+            if (c) { stack_flush(&s); return c; }
+        } else {
+            stack_push(&s, c0->left);
+            stack_push(&s, c1->left);
+            stack_push(&s, c0->right);
+            stack_push(&s, c1->right);
+        }
+    }
 }