diff --git a/03/type.cpp b/03/type.cpp
index 206a9aa..91f87d3 100644
--- a/03/type.cpp
+++ b/03/type.cpp
@@ -3,18 +3,17 @@
 #include <algorithm>
 
 std::string type_mgr::new_type_name() {
-    std::ostringstream oss;
     int temp = last_id++;
+    std::string str = "";
 
-    do {
-        oss << (char) ('a' + (temp % 26));
-        temp /= 26;
-    } while(temp);
-    std::string str = oss.str();
+    while(temp != -1) {
+        str += (char) ('a' + (temp % 26));
+        temp = temp / 26 - 1;
+    }
 
     std::reverse(str.begin(), str.end());
     return str;
-};
+}
 
 type_ptr type_mgr::new_type() {
     return type_ptr(new type_var(new_type_name()));
@@ -23,3 +22,57 @@ type_ptr type_mgr::new_type() {
 type_ptr type_mgr::new_arrow_type() {
     return type_ptr(new type_arr(new_type(), new_type()));
 }
+
+type_ptr type_mgr::resolve(type_ptr t, type_var*& var) {
+    type_var* cast;
+
+    var = nullptr;
+    while((cast = dynamic_cast<type_var*>(t.get()))) {
+        auto it = types.find(cast->name);
+
+        if(it == types.end()) {
+            var = cast;
+            break;
+        }
+        t = it->second;
+    }
+
+    return t;
+}
+
+void type_mgr::unify(type_ptr l, type_ptr r) {
+    type_var* lvar;
+    type_var* rvar;
+    type_arr* larr;
+    type_arr* rarr;
+    type_base* lid;
+    type_base* rid;
+
+    l = resolve(l, lvar);
+    r = resolve(r, rvar);
+
+    if(lvar) {
+        bind(lvar->name, r);
+        return;
+    } else if(rvar) {
+        bind(rvar->name, l);
+        return;
+    } else if((larr = dynamic_cast<type_arr*>(l.get())) &&
+            (rarr = dynamic_cast<type_arr*>(r.get()))) {
+        unify(larr->left, rarr->left);
+        unify(larr->right, rarr->right);
+        return;
+    } else if((lid = dynamic_cast<type_base*>(l.get())) &&
+            (rid = dynamic_cast<type_base*>(r.get()))) {
+        if(lid->name == rid->name) return;
+    }
+
+    throw 0;
+}
+
+void type_mgr::bind(std::string s, type_ptr t) {
+    type_var* other = dynamic_cast<type_var*>(t.get());
+    
+    if(other && other->name == s) return;
+    types[s] = t;
+}
diff --git a/03/type.hpp b/03/type.hpp
index 752d778..ab358a4 100644
--- a/03/type.hpp
+++ b/03/type.hpp
@@ -15,11 +15,11 @@ struct type_var : public type {
         : name(std::move(n)) {}
 };
 
-struct type_id : public type {
-    int id;
+struct type_base : public type {
+    std::string name;
 
-    type_id(int i) 
-        : id(i) {}
+    type_base(std::string n) 
+        : name(std::move(n)) {}
 };
 
 struct type_arr : public type {
@@ -32,8 +32,13 @@ struct type_arr : public type {
 
 struct type_mgr {
     int last_id = 0;
+    std::map<std::string, type_ptr> types;
 
     std::string new_type_name();
     type_ptr new_type();
     type_ptr new_arrow_type();
+
+    void unify(type_ptr l, type_ptr r);
+    type_ptr resolve(type_ptr t, type_var*& var);
+    void bind(std::string s, type_ptr t);
 };