diff --git a/assignments/PA4/bad_inherit.cl b/assignments/PA4/bad_inherit.cl
index 7d28689..ba6b40f 100644
--- a/assignments/PA4/bad_inherit.cl
+++ b/assignments/PA4/bad_inherit.cl
@@ -29,17 +29,20 @@ class Ok4 inherits Ok2_2 {};
 
 (* Cool has restrictions on inheriting from basic classes *)
 
-class Err1 inherits Int {};
+(*class Err1 inherits Int {};
 class Err3 inherits String {};
 class Err3 inherits Bool {};
-class Err4 inherits Err3 {};
-class Err4 inherits NOEXIST {};
+class Err4 inherits Err3 {};*)
+class Err4 inherits Ok1 {
+    bye: SS <- 10;
+    hello(a: TT) : NOEXIST { new Object };
+};
 
 
 class Main inherits IO {
     main(): Object {
         {
-            a();
+            (new Err4).hell();
         }
     };
 };
\ No newline at end of file
diff --git a/assignments/PA4/cool-tree.h b/assignments/PA4/cool-tree.h
index 6c4223d..79f93bf 100644
--- a/assignments/PA4/cool-tree.h
+++ b/assignments/PA4/cool-tree.h
@@ -164,6 +164,7 @@ public:
    Symbol get_name() const { return name; }
    Symbol get_parent() const { return parent; }
    Features get_features() const { return features; }
+   void semant();
 
 #ifdef Class__SHARED_EXTRAS
    Class__SHARED_EXTRAS
@@ -191,6 +192,11 @@ public:
    Feature copy_Feature();
    void dump(ostream& stream, int n);
 
+   Symbol get_name() const { return name; };
+   Formals get_formals() const { return formals; };
+   Symbol get_return_type() const { return return_type; };
+   Expression get_expr() const { return expr; };
+
 #ifdef Feature_SHARED_EXTRAS
    Feature_SHARED_EXTRAS
 #endif
@@ -215,6 +221,10 @@ public:
    Feature copy_Feature();
    void dump(ostream& stream, int n);
 
+   Symbol get_name() const { return name; };
+   Symbol get_type_decl() const { return type_decl; };
+   Expression get_init() const { return init; };
+
 #ifdef Feature_SHARED_EXTRAS
    Feature_SHARED_EXTRAS
 #endif
diff --git a/assignments/PA4/semant.cc b/assignments/PA4/semant.cc
index 56cf5ac..c4a9fbd 100644
--- a/assignments/PA4/semant.cc
+++ b/assignments/PA4/semant.cc
@@ -86,9 +86,14 @@ static void initialize_constants(void)
 }
 
 
-
+/*
+*   In ClassTable's constructor, the inheritance graph is built and checked, 
+*      with all defined classes recorded for later check.
+*   In addition, scan attribute and method definition into global Symbol Table
+*/
 ClassTable::ClassTable(Classes classes) : semant_errors(0) , error_stream(cerr) {
     install_basic_classes();
+    /* first scan: de-duplicate class definitions*/
     std::vector<class__class* > class_vec;
     for (auto i = classes->first(); classes->more(i); i = classes->next(i)) {
         auto class_i = static_cast<class__class*>(classes->nth(i));
@@ -96,12 +101,14 @@ ClassTable::ClassTable(Classes classes) : semant_errors(0) , error_stream(cerr)
             semant_error(class_i) << "Class " << class_i->get_name() << " was previously defined.\n";
         }
         else {
-            name_to_node[class_i->get_name()] = new ClassGraphNode(class_i, nullptr);
             // null means we have this class, but not yet build inheritence graph for it
+            name_to_node[class_i->get_name()] = new ClassGraphNode(class_i, nullptr);
+            // discard redefined classes by constructing a new vector of classes
             class_vec.push_back(class_i);
         }
     }
 
+    /* second scan: check base class inheritable */
     auto sym_Bool = idtable.lookup_string("Bool");
     auto sym_Int = idtable.lookup_string("Int");
     auto sym_String = idtable.lookup_string("String");
@@ -130,6 +137,8 @@ ClassTable::ClassTable(Classes classes) : semant_errors(0) , error_stream(cerr)
     // In COOL's case, every class could have only one base class
     // One simple judgement is that, if it cannot go up to object, then the class or its ancestor involves in a cycle
     // Thus, we can start from object and mark all reachable nodes, error report those unreachable nodes
+
+    /* third scan: check cyclic inheritance */
     class_root->traverse();
     for (auto i : name_to_node) {
         if (!i.second->reachable()) {
@@ -139,9 +148,41 @@ ClassTable::ClassTable(Classes classes) : semant_errors(0) , error_stream(cerr)
     }
     if (semant_errors) return;
     if (semant_debug) {
-        std::cout << "Class Inheritance Analysis done.\n";
+        std::cerr<< "Class Inheritance Analysis done.\n";
         class_root->traverse(std::cout, 0);
     }
+    /* fourth scan: gather attr and method definition */
+    for (auto class_i : class_vec) {
+        auto features_i = class_i->get_features();
+        auto name_i = class_i->get_name();
+        symtab_met[name_i] = new SymbolTable<Symbol, method_class>;
+        symtab_obj[name_i] = new SymbolTable<Symbol, Entry>;
+        symtab_met[name_i]->enterscope();
+        symtab_obj[name_i]->enterscope();
+        for (auto j = features_i->first(); features_i->more(j); j = features_i->next(j)) {
+            auto feature_j = features_i->nth(j);
+            if (typeid(*feature_j) == typeid(attr_class)) {
+                auto attr_j = static_cast<attr_class*>(feature_j);
+                symtab_obj[name_i]->addid(attr_j->get_name(), attr_j->get_type_decl());
+            }
+            else if (typeid(*feature_j) == typeid(method_class)) {
+                auto method_j = static_cast<method_class*>(feature_j);
+                symtab_met[name_i]->addid(method_j->get_name(), method_j);
+            }
+            else assert(0);
+        }
+    }
+    if (semant_debug) {
+        std::cerr << "Attr & Methods Collection done.\n";
+        for (auto class_i : class_vec) {
+            auto name_i = class_i->get_name();
+            std::cerr << "M(" << name_i << ") =";
+            symtab_met[name_i]->dump();
+            std::cerr << "O(" << name_i << ") =";
+            symtab_obj[name_i]->dump();
+            std::cerr << "--------\n\n";
+        }
+    }
 }
 
 void ClassTable::install_basic_classes() {
@@ -316,6 +357,15 @@ void program_class::semant()
     /* ClassTable constructor may do some semantic analysis */
     ClassTable *classtable = new ClassTable(classes);
 
+    /* Without confidence in inheritance consistency, abort before type checking*/
+    if (classtable->errors()) {
+	cerr << "Compilation halted due to static semantic errors." << endl;
+	exit(1);
+    }
+    for (auto i = classes->first(); classes->more(i); i = classes->next(i)) {
+        auto class_i = static_cast<class__class*>(classes->nth(i));
+        class_i->semant();
+    }
     /* some semantic analysis code may go here */
 
     if (classtable->errors()) {
@@ -324,4 +374,7 @@ void program_class::semant()
     }
 }
 
-
+void class__class::semant()
+{
+    
+}
diff --git a/assignments/PA4/semant.h b/assignments/PA4/semant.h
index e8c6694..c66946d 100644
--- a/assignments/PA4/semant.h
+++ b/assignments/PA4/semant.h
@@ -125,6 +125,10 @@ private:
   //  anyways we don't need name shadowing here, I just save my effort
   std::map<Symbol, ClassGraphNode*> name_to_node;
 
+  // The symbol table only stores pointers, so DATA type defined here dont need a ptr
+  std::map<Symbol, SymbolTable<Symbol, Entry>* > symtab_obj;
+  std::map<Symbol, SymbolTable<Symbol, method_class>*> symtab_met;
+
 public:
   ClassTable(Classes);
   int errors() { return semant_errors; }