On the product of derivatives
Volume 80 / 1973
                    
                    
                        Fundamenta Mathematicae 80 (1973), 293-294                    
                                        
                        DOI: 10.4064/fm-80-3-293-294                    
                                    
                                                                
                             
             
                                                             
                                                             
                                                             
                                                             
                                                             
                                                             
                                                         
                                                            