First, core.reducers requires clojure.walk :as walk, but does not use the alias.
Second, the two arity implementation of coll-reduce in function reducer uses 'this', whereas similar implementations in that file use 'coll'. AFAICT it makes no difference to use 'coll' (all tests pass, no change in performance) and it is more in line with the rest of the code.
The two things seem small enough to be put into one cleanup case.
