;; • Generate an error message by evaluating an appropriate symbol that
;; is not within parentheses.
+

;; • Generate an error message by evaluating an appropriate symbol that
;; is between parentheses.
(0)

;; • Create a counter that increments by two rather than one.
(setq counter 0)
(setq counter (+ counter 2))
counter

;; • Write an expression that prints a message in the echo area when
;; evaluated.
(message "A message.")
