Understanding Clojure reduce better

Code

(defn add [a b]
  (+ a b))

(reduce add [1 2 3 4 5])

(reduce add 1 [2 3 4 5])

(reduce add 3 [3 4 5])

;; (reduce add [3 3 4 5])

(reduce add 3 [3 4 5])

(reduce add 6 [4 5])

(reduce add 10 [5])

(remove #(= % :a) [:a :b :c :d])

(defn remove-value [seq value]
  (remove #(= % value) seq))

(remove-value [:a :b :c :d] :b)

(reduce remove-value [:a :b :c :d] [:b :d])

(reduce remove-value [:a :b :c :d] [:b])

(reduce remove-value [:a :c :d] [:d])

(reduce remove-value [:a :c] [])