+ (let ((str (write-to-string num :readably t)))
+ (cond
+ ((find #\f str)
+ (substitute #\e #\f str))
+ ((find #\d str)
+ (substitute #\e #\d str))
+ ((find #\F str)
+ (substitute #\e #\F str))
+ ((find #\D str)
+ (substitute #\e #\D str))
+ ((find #\S str)
+ (substitute #\e #\S str))
+ (t
+ str))))