The
            following predefined variables are commonly used in AutoLISP applications:
         
- PAUSE
 
            - 
               
                  Defined as a string consisting of a double backslash
                     (\\) character. This variable is used with the command function to
                     pause for user input.
                  
                
             - PI
 
            - 
               
                  Defined as the constant p (pi). It evaluates
                     to approximately 3.14159.
                  
                
             - T
 
            - 
               
                  Defined as the constant T.
                     This is used as a non-nil value.
                  
                
             
         
         NoteYou
               can change the value of these variables with the setq function. However,
               other applications might rely on their values being consistent;
               therefore, it is recommended that you do not modify these variables.
               Visual LISP, by default, protects these variables from redefinition.
               You can override this protection through the VLISP Symbol Service
               feature or by setting a VLISP environment option.