We can think of a symbol as a data structure that includes a value cell containing a pointer to the value of the atom. The value of the symbol can be set using the function SET:
(SET 'PRESIDENT 'JEFFERSON)If we now evaluate PRESIDENT, we get the value JEFFERSON.
Since the first argument of SET is usually quoted, there is a special function SETQ that does this automatically.
(SETQ PRESIDENT 'JEFFERSON) (SETQ RADIUS 5.0) (* PI (EXPT RADIUS 2))