(setf emptystring "") ;binds variable'emptystring' to the empty string ""

(let ((emptystring "")) ;; Binds local variable 'emptystring' to the empty string ""
  (when (string-equal emptystring "")  ;;case insensitive string comparison
    (print "Is an empty string"))  ;;bad argument error if not a string
  (when (stringp emptystring)
    (print "Is a string"))
  (when (not (stringp emptystring))
    (print "Is not a string"))
  (when (and (stringp emptystring)(= (length emptystring) 0))
    (print "Is an empty string"))
  (when (and (stringp emptystring)(> (length emptystring) 0))
    (print "Is a non-empty string")))