(not x)
Returns true if x is logical false, false otherwise.
user=> (not true)
false
user=> (not false)
true
user=> (not nil)
true
;; acts as complement of `boolean`
user=> (boolean "a string")
true
user=> (not "a string")
false
user=> (boolean 1)
true
user=> (not 1)
false
user=> (not (= "a" "b"))
true