I was always under the impression that Sets aren't ordered, but noticed that Sets of Characters do seem to be ordered:
(seq #{\e \c \b \z \a})
=> (\a \b \c \e \z)
If I introduce other kinds of characters, it seems as though they're being ordered according to the codes of the characters:
(seq #{\e \A \c \space \b \z \a})
=> (\space \A \a \b \c \e \z)
Why are characters being sorted according to their code, but Sets of numbers appear to have arbitrary ordering?