user=> (defn foo [] 123)
#'user/foo
user=> (def bar foo)
#'user/bar
user=> (bar)
123
user=> (defn foo [] 999)
#'user/foo
user=> (bar)
123
user=> (def bar #'foo)
#'user/bar
user=> (bar)
999
user=> (defn foo [] 123)
#'user/foo
user=> (bar)
123
user=>