Lecture 20:

                                           Arithmetic II

                                    Politeness in Correspondence

                                           Arithmetic II

                                           Arithmetic II

                                           Arithmetic II

                                           Arithmetic II

                                           Arithmetic II

                                           Arithmetic II

                                    Politeness in Correspondence

                                    Politeness in Correspondence

                                    Politeness in Correspondence

                                    Politeness in Correspondence

                                              Homework