Some commonly used sets and their standard notations

• Set of natural numbers    ---         N.
                            
• Set of integers                 ---        .
                           
• Set of rational numbers   ---         Q.
                           
• Set of real numbers         ---         .
                           
• Set of complex numbers  ---         C.
                           
• Open interval on the real line
                                        
• Closed interval on the real line
                                        
• Semi open intervals