diff --git a/ColoredSquare.c b/ColoredSquare.c
deleted file mode 100644
index 06a229b..0000000
--- a/ColoredSquare.c
+++ /dev/null
@@ -1,106 +0,0 @@
-#include <stdlib.h>
-#include <stdio.h>
-
-#include "ColoredSquare.h"
-
-void ColoredSquare_constructor (ColoredSquare *this,
-                                double a,
-                                int color)
-{
-  printf ("ColoredSquare_constructor (%lu, %f, %d) called\n",
-          (unsigned long) this,
-          a,
-          color);
-  Square_constructor ((Square *) this, a);
-  this->color = color;
-}
-
-void ColoredSquare_copy (ColoredSquare *dest, const ColoredSquare *src)
-{
-  printf ("ColoredSquare_copy (%lu, %lu) called\n",
-          (unsigned long) dest,
-          (unsigned long) src);
-  Square_copy ((Square *) dest, (Square *) src);
-  dest->color = src->color;
-}
-
-ColoredSquare* ColoredSquare_clone (const ColoredSquare *this)
-{
-  ColoredSquare *csquare = ColoredSquare_new (0.0, 0);
-  printf ("ColoredSquare_clone (%lu) called\n",
-          (unsigned long) this);
-  ColoredSquare_copy (csquare, this);
-  printf ("ColoredSquare_clone (%lu) returns %lu\n",
-          (unsigned long) this,
-          (unsigned long) csquare);
-
-  return csquare;
-}
-
-const char* ColoredSquare_type (const ColoredSquare *this)
-{
-  static const char *csquare_type_str = "ColoredSquare";
-  printf ("ColoredSquare_type (%lu) called\n",
-          (unsigned long) this);
-  printf ("ColoredSquare_type (%lu) returns \"%s\"\n",
-          (unsigned long) this,
-          csquare_type_str);
-  return csquare_type_str;
-}
-
-void ColoredSquare_draw (const ColoredSquare *this)
-{
-  printf ("ColoredSquare_draw (%lu) called\n",
-          (unsigned long) this);
-  printf ("Drawing ColoredSquare with %f side and %d color\n",
-          this->a,
-          this->color);
-}
-
-void ColoredSquare_set_color (ColoredSquare *this, int color)
-{
-  printf ("ColoredSquare_draw (%lu, %d) called\n",
-          (unsigned long) this,
-          color);
-
-  this->color = color;
-}
-
-/* public */
-ColoredSquare* ColoredSquare_new (double a, int color)
-{
-  static ColoredSquare_interface vtable =
-    {
-      {
-        {
-          {
-            (void* (*) (const void *)) ColoredSquare_clone,
-            (void (*) (void *)) Square_destroy
-          },
-          (const char* (*) (const Figure *)) ColoredSquare_type,
-          (void (*) (const Figure *)) ColoredSquare_draw,
-          (double (*) (const Figure *)) Square_area
-        },
-        Square_resize,
-        Square_diag_length
-      },
-      ColoredSquare_set_color
-    };
-  ColoredSquare *square = malloc (sizeof (*square));
-
-  ColoredSquare_constructor (square, a, color);
-
-  printf ("ColoredSquare_new (%f, %d) returns %lu\n",
-          a,
-          color,
-          (unsigned long) square); 
-
-  square->vtable = &vtable;
-
-/*goto end;
-err:
-
-end:*/
-
-  return square;
-}
diff --git a/ColoredSquare.h b/ColoredSquare.h
deleted file mode 100644
index fc54ba1..0000000
--- a/ColoredSquare.h
+++ /dev/null
@@ -1,44 +0,0 @@
-#ifndef __COLORED_SQUARE_H__
-#define __COLORED_SQUARE_H__
-
-#include "Square.h"
-
-typedef struct ColoredSquare_data
-{
-  Square_data;
-
-  int color;
-
-} ColoredSquare_data;
-
-struct ColoredSquare;
-
-typedef struct ColoredSquare_interface
-{
-  Square_interface;
-
-  void (*set_color) (struct ColoredSquare *this, int color);
-
-} ColoredSquare_interface;
-
-void ColoredSquare_constructor (struct ColoredSquare *this,
-                                double a,
-                                int color);
-void ColoredSquare_copy (struct ColoredSquare *dest, const struct ColoredSquare *src);
-struct ColoredSquare* ColoredSquare_clone (const struct ColoredSquare *this);
-const char* ColoredSquare_type (const struct ColoredSquare *this);
-void ColoredSquare_draw (const struct ColoredSquare *this);
-void ColoredSquare_set_color (struct ColoredSquare *this, int color);
-
-/* public */
-typedef struct ColoredSquare
-{
-  ColoredSquare_interface *vtable;
-
-  ColoredSquare_data;
-
-} ColoredSquare;
-
-ColoredSquare* ColoredSquare_new (double a, int color);
-
-#endif // __COLORED_SQUARE_H__
diff --git a/Figure.c b/Figure.c
new file mode 100644
index 0000000..425b42c
--- /dev/null
+++ b/Figure.c
@@ -0,0 +1,17 @@
+#include "Figure.h"
+
+/* considered to be protected */
+void Figure_constructor (Figure *this)
+{
+  // nothin here
+}
+
+void Figure_destructor (Figure *this)
+{
+  // nothin here
+}
+
+void Figure_copy (struct Figure *dest, const struct Figure *src)
+{
+  // nothin here
+}
diff --git a/Figure.h b/Figure.h
index 7a0eecc..0679cbf 100644
--- a/Figure.h
+++ b/Figure.h
@@ -3,22 +3,47 @@
 
 #include "Object.h"
 
-struct Figure;
-
-typedef struct Figure_interface
-{
-  Object_interface;
-
-  const char* (*type) (const struct Figure *this);
-  void (*draw) (const struct Figure *this);
-  double (*area) (const struct Figure *this);
-
-} Figure_interface;
-
 typedef struct Figure
 {
-  Figure_interface *vtable;
+  struct Figure_vtable
+  {
+    /* derived from Object */
+    const char* (*type) ();
+    struct Figure* (*clone) (const struct Figure *this);
+    void (*destroy) (struct Figure *this);
+
+    /* Figure virtual methods */
+    void (*draw) (const struct Figure *this);
+    double (*area) (const struct Figure *this);
+
+  } *vtable;
 
 } Figure;
 
+static inline const char* Figure_type (const Figure *this)
+{
+  return this->vtable->type ();
+}
+static inline Figure* Figure_clone (const Figure *this)
+{
+  return this->vtable->clone (this);
+}
+static inline void Figure_destroy (Figure *this)
+{
+  this->vtable->destroy (this);
+}
+static inline void Figure_draw (const struct Figure *this)
+{
+  this->vtable->draw (this);
+}
+static inline double (*area) (const struct Figure *this)
+{
+  return this->vtable->area (this);
+}
+
+/* considered to be protected */
+void Figure_constructor (Figure *this);
+void Figure_destructor (Figure *this);
+void Figure_copy (struct Figure *dest, const struct Figure *src);
+
 #endif // __FIGURE_H__
diff --git a/Object.h b/Object.h
index 66a1d08..89670c1 100644
--- a/Object.h
+++ b/Object.h
@@ -1,11 +1,17 @@
 #ifndef __OBJECT_H__
 #define __OBJECT_H__
 
-typedef struct Object_interface
+typedef struct Object
 {
-  void* (*clone) (const void *this);
-  void (*destroy) (void *this);
+  struct Object_vtable
+  {
+    /* Object methods */
+    const char* (*type) ();
+    struct Object* (*clone) (const Object *this);
+    void (*destroy) (struct Object *this);
+  
+  } *vtable;
 
-} Object_interface;
+} Object;
 
 #endif // __OBJECT_H__
diff --git a/Polygon.h b/Polygon.h
new file mode 100644
index 0000000..440bf0b
--- /dev/null
+++ b/Polygon.h
@@ -0,0 +1,70 @@
+#ifndef __POLYGON_H__
+#define __POLYGON_H__
+
+#include "Figure.h"
+
+typedef struct Polygon
+{
+  struct Polygon_vtable
+  {
+    /* derived from Object */
+    const char* (*type) ();
+    struct Polygon* (*clone) (const struct Polygon *this);
+    void (*destroy) (struct Polygon *this);
+
+    /* derived from Figure */
+    void (*draw) (const struct Polygon *this);
+    double (*area) (const struct Polygon *this);
+
+    /* Polygon virtual methods */
+    double (*max_diag) (const struct Polygon *this);
+
+  } *vtable;
+
+  /* Polygon fields */
+  struct point
+  {
+    double x, y;
+  
+  } *points;
+
+} Polygon;
+
+Polygon* Polygon_new (const struct *points);
+
+static inline const char* Polygon_type (const Polygon *this)
+{
+  return this->vtable->type ();
+}
+
+static inline Polygon* Polygon_clone (const Polygon *this)
+{
+  return this->vtable->clone (this);
+}
+
+static inline void Polygon_destroy (Polygon *this)
+{
+  this->vtable->destroy (this);
+}
+
+static inline void Polygon_draw (const Polygon *this)
+{
+  this->vtable->draw (this);
+}
+
+static inline double Polygon_area (const Polygon *this)
+{
+  return this->vtable->area (this);
+}
+
+static inline double Polygon_max_diag (const Polygon *this)
+{
+  return this->max_diag (this);
+}
+
+/* considered to be protected */
+void Polygon_constructor (Polygon *this);
+void Polygon_destructor (Polygon *this);
+void Polygon_copy (Polygon *dest, const Polygon *src);
+
+#endif // __POLYGON_H__
diff --git a/Rhomb.h b/Rhomb.h
new file mode 100644
index 0000000..d090337
--- /dev/null
+++ b/Rhomb.h
@@ -0,0 +1,75 @@
+#ifndef __RHOMB_H__
+#define __RHOMB_H__
+
+#include "Polygon.h"
+
+typedef struct Rhomb
+{
+  struct Rhomb_vtable
+  {
+    /* derived from Object */
+    const char* (*type) ();
+    struct Rhomb* (*clone) (const struct Rhomb *this);
+    void (*destroy) (struct Rhomb *this);
+
+    /* derived from Figure */
+    void (*draw) (const struct Rhomb *this);
+    double (*area) (const struct Rhomb *this);
+
+    /* derived from Polygon */
+    double (*max_diag) (const struct Rhomb *this);
+
+    /* Rhomb virtual methods */
+    int (*is_square) (const struct Rhomb *this);
+
+  } *vtable;
+
+  /* derived from Polygon */
+  struct point
+  {
+    double x, y;
+  
+  } *points;
+
+} Rhomb;
+
+Rhomb* Rhomb_new (const struct *points);
+
+static inline const char* Rhomb_type (const Rhomb *this)
+{
+  return this->vtable->type ();
+}
+
+static inline Rhomb* Rhomb_clone (const Rhomb *this)
+{
+  return this->vtable->clone (this);
+}
+
+static inline void Rhomb_destroy (Rhomb *this)
+{
+  this->vtable->destroy (this);
+}
+
+static inline void Rhomb_draw (const Rhomb *this)
+{
+  this->vtable->draw (this);
+}
+
+static int double Rhomb_area (const Rhomb *this)
+{
+  return this->vtable_area (this);
+}
+
+static inline double Rhomb_max_diag (const Rhomb *this)
+{
+  return this->max_diag (this);
+}
+
+static inline int Rhomb_is_square (const Rhomb *this);
+
+/* considered to be protected */
+void Rhomb_constructor (Rhomb *this);
+void Rhomb_destructor (Rhomb *this);
+void Rhomb_copy (Rhomb *dest, const Rhomb *src);
+
+#endif // __RHOMB_H__
diff --git a/Square.c b/Square.c
deleted file mode 100644
index 558ae6b..0000000
--- a/Square.c
+++ /dev/null
@@ -1,134 +0,0 @@
-#include <stdlib.h>
-#include <stdio.h>
-
-#include "Square.h"
-
-void Square_constructor (Square *this, double a)
-{
-  printf ("Square_constructor (%lu, %f) called\n",
-          (unsigned long) this,
-          a);
-  this->a = a;
-}
-
-void Square_destructor (Square *this)
-{
-  printf ("Square_destructor (%lu) called\n",
-          (unsigned long) this);
-}
-
-void Square_copy (Square *dest, const Square *src)
-{
-  printf ("Square_copy (%lu, %lu) called\n",
-          (unsigned long) dest,
-          (unsigned long) src);
-  dest->a = src->a;
-}
-
-Square* Square_clone (const Square *this)
-{
-  Square *square = Square_new (0.0);
-  printf ("Square_clone (%lu) called\n",
-          (unsigned long) this);
-  Square_copy (square, this);
-  printf ("Square_clone (%lu) returns %lu\n",
-          (unsigned long) this,
-          (unsigned long) square);
-
-  return square;
-}
-
-void Square_destroy (Square *this)
-{
-  printf ("Square_destroy (%lu) called\n",
-          (unsigned long) this);
-  free (this);
-}
-
-const char* Square_type (const Square *this)
-{
-  static const char *square_type_str = "Square";
-  printf ("Square_type (%lu) called\n",
-          (unsigned long) this);
-  printf ("Square_type (%lu) returns \"%s\"\n",
-          (unsigned long) this,
-          square_type_str);
-
-  return square_type_str;
-}
-
-void Square_draw (const Square *this)
-{
-  printf ("Square_draw (%lu) called\n",
-          (unsigned long) this);
-  printf ("Drawing Square with %f side\n",
-          this->a);
-}
-
-double Square_area (const Square *this)
-{
-  double area = this->a * this->a;
-  printf ("Square_area (%lu) called\n",
-          (unsigned long) this);
-  printf ("Square_area (%lu) returns %f\n",
-          (unsigned long) this,
-          area);
-
-  return area;
-}
-
-void Square_resize (Square *this, double a)
-{
-  printf ("Square_resize (%lu, %f) called\n",
-          (unsigned long) this,
-          a);
-  this->a = a;
-}
-
-double Square_diag_length (const Square *this)
-{
-  double diag_length = ((Square *)this)->a * 1.41421356;
-
-  printf ("Square_diag_length (%lu) called\n",
-          (unsigned long) this);
-  printf ("Square_diag_length (%lu) returns %f\n",
-          (unsigned long) this,
-          diag_length);
-
-  return diag_length;
-}
-
-/* public */
-Square* Square_new (double a)
-{
-  static Square_interface vtable =
-    {
-      {
-        {
-          (void* (*) (const void *)) Square_clone,
-          (void (*) (void *)) Square_destroy
-        },
-        (const char* (*) (const Figure *)) Square_type,
-        (void (*) (const Figure *)) Square_draw,
-        (double (*) (const Figure *)) Square_area
-      },
-      Square_resize,
-      Square_diag_length
-    };
-  Square *square = malloc (sizeof (*square));
-
-  Square_constructor (square, a);
-
-  printf ("Square_new (%f) returns %lu\n",
-          a,
-          (unsigned long) square); 
-
-  square->vtable = &vtable;
-
-/*goto end;
-err:
-
-end:*/
-
-  return square;
-}
diff --git a/Square.h b/Square.h
deleted file mode 100644
index 49c057f..0000000
--- a/Square.h
+++ /dev/null
@@ -1,45 +0,0 @@
-#ifndef __SQUARE_H__
-#define __SQUARE_H__
-
-#include "Figure.h"
-
-typedef struct Square_data
-{
-  double a;
-
-} Square_data;
-
-struct Square;
-
-typedef struct Square_interface
-{
-  Figure_interface;
-
-  void (*resize) (struct Square *this, double a);
-  double (*diag_length) (const struct Square *this);
-
-} Square_interface;
-
-void Square_constructor (struct Square *this, double a);
-void Square_destructor (struct Square *this);
-void Square_copy (struct Square *dest, const struct Square *src);
-struct Square* Square_clone (const struct Square *this);
-void Square_destroy (struct Square *this);
-const char* Square_type (const struct Square *this);
-void Square_draw (const struct Square *this);
-double Square_area (const struct Square *this);
-void Square_resize (struct Square *this, double a);
-double Square_diag_length (const struct Square *this);
-
-/* public */
-typedef struct Square
-{
-  Square_interface *vtable;
-
-  Square_data;
-
-} Square;
-
-Square* Square_new (double a);
-
-#endif // __SQUARE_H__