Something

               foreach (object command in faces[num].command) {
                      int k;

                      if (command is vertex)
                      {
                         System.Console.WriteLine( command.x );
                      }
                  }

'object' does not contain a definition for 'x' and no extension method 'x' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?)