There's a "b" in "about", but there's no "k" or "m".
(def phrase "Fjord zoologists quip jovially, waxing lyrical about xanthic lutrines")
(require '[clojure.string :as str])
(-> phrase str/lower-case distinct sort)
;; => (\space \, \a \b \c \d \e \f \g \h \i \j \l \n \o \p \q \r \s \t \u \v \w \x \y \z)
>>> phrase = "Fjord zoologists quip jovially, waxing lyrical about xanthic lutrines"
>>> import string
>>> set(string.ascii_lowercase) - set(phrase.lower())
{'k', 'm'}