diff --git a/code/compiler/11/parsed_type.cpp b/code/compiler/11/parsed_type.cpp
index ba6fddd..4644d52 100644
--- a/code/compiler/11/parsed_type.cpp
+++ b/code/compiler/11/parsed_type.cpp
@@ -21,7 +21,7 @@ type_ptr parsed_type_app::to_type(
 type_ptr parsed_type_var::to_type(
         const std::set<std::string>& vars,
         const type_env& e) const {
-    if(vars.find(var) != vars.end()) throw 0;
+    if(vars.find(var) == vars.end()) throw 0;
     return type_ptr(new type_var(var));
 }
 
diff --git a/code/compiler/11/type.cpp b/code/compiler/11/type.cpp
index 6c381b8..8022966 100644
--- a/code/compiler/11/type.cpp
+++ b/code/compiler/11/type.cpp
@@ -16,43 +16,13 @@ void type_scheme::print(const type_mgr& mgr, std::ostream& to) const {
     monotype->print(mgr, to);
 }
 
-type_ptr substitute(const type_mgr& mgr, const std::map<std::string, type_ptr>& subst, const type_ptr& t) {
-    type_var* var;
-    type_ptr resolved = mgr.resolve(t, var);
-    if(var) {
-        auto subst_it = subst.find(var->name);
-        if(subst_it == subst.end()) return resolved;
-        return subst_it->second;
-    } else if(type_arr* arr = dynamic_cast<type_arr*>(t.get())) {
-        auto left_result = substitute(mgr, subst, arr->left);
-        auto right_result = substitute(mgr, subst, arr->right);
-        if(left_result == arr->left && right_result == arr->right) return t;
-        return type_ptr(new type_arr(left_result, right_result));
-    } else if(type_app* app = dynamic_cast<type_app*>(t.get())) {
-        auto constructor_result = substitute(mgr, subst, app->constructor);
-        bool arg_changed = false;
-        std::vector<type_ptr> new_args;
-        for(auto& arg : app->arguments) {
-            auto arg_result = substitute(mgr, subst, arg);
-            arg_changed |= arg_result != arg;
-            new_args.push_back(std::move(arg_result));
-        }
-
-        if(constructor_result == app->constructor && !arg_changed) return t;
-        type_app* new_app = new type_app(std::move(constructor_result));
-        std::swap(new_app->arguments, new_args);
-        return type_ptr(new_app);
-    }
-    return t;
-}
-
 type_ptr type_scheme::instantiate(type_mgr& mgr) const {
     if(forall.size() == 0) return monotype;
     std::map<std::string, type_ptr> subst;
     for(auto& var : forall) {
         subst[var] = mgr.new_type();
     }
-    return substitute(mgr, subst, monotype);
+    return mgr.substitute(subst, monotype);
 }
 
 void type_var::print(const type_mgr& mgr, std::ostream& to) const {
@@ -161,6 +131,39 @@ void type_mgr::unify(type_ptr l, type_ptr r) {
     throw unification_error(l, r);
 }
 
+type_ptr type_mgr::substitute(const std::map<std::string, type_ptr>& subst, const type_ptr& t) const {
+    type_ptr temp = t;
+    while(type_var* var = dynamic_cast<type_var*>(temp.get())) {
+        auto subst_it = subst.find(var->name);
+        if(subst_it != subst.end()) return subst_it->second;
+        auto var_it = types.find(var->name);
+        if(var_it == types.end()) return t;
+        temp = var_it->second;
+    }
+
+    if(type_arr* arr = dynamic_cast<type_arr*>(temp.get())) {
+        auto left_result = substitute(subst, arr->left);
+        auto right_result = substitute(subst, arr->right);
+        if(left_result == arr->left && right_result == arr->right) return t;
+        return type_ptr(new type_arr(left_result, right_result));
+    } else if(type_app* app = dynamic_cast<type_app*>(temp.get())) {
+        auto constructor_result = substitute(subst, app->constructor);
+        bool arg_changed = false;
+        std::vector<type_ptr> new_args;
+        for(auto& arg : app->arguments) {
+            auto arg_result = substitute(subst, arg);
+            arg_changed |= arg_result != arg;
+            new_args.push_back(std::move(arg_result));
+        }
+
+        if(constructor_result == app->constructor && !arg_changed) return t;
+        type_app* new_app = new type_app(std::move(constructor_result));
+        std::swap(new_app->arguments, new_args);
+        return type_ptr(new_app);
+    }
+    return t;
+}
+
 void type_mgr::bind(const std::string& s, type_ptr t) {
     type_var* other = dynamic_cast<type_var*>(t.get());
     
diff --git a/code/compiler/11/type.hpp b/code/compiler/11/type.hpp
index cd3bd45..6c524aa 100644
--- a/code/compiler/11/type.hpp
+++ b/code/compiler/11/type.hpp
@@ -86,6 +86,9 @@ struct type_mgr {
     type_ptr new_arrow_type();
 
     void unify(type_ptr l, type_ptr r);
+    type_ptr substitute(
+            const std::map<std::string, type_ptr>& subst,
+            const type_ptr& t) const;
     type_ptr resolve(type_ptr t, type_var*& var) const;
     void bind(const std::string& s, type_ptr t);
     void find_free(const type_ptr& t, std::set<std::string>& into) const;