diff --git a/.travis.yml b/.travis.yml
index 455f3c0..45c29f6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,6 @@
 language: clojure
-lein: lein2
-script: lein2 midje :config .midje-grading-config.clj
+lein: lein
+script: lein midje :config .midje-grading-config.clj
 jdk:
   - openjdk7
 notifications:
diff --git a/src/recursion.clj b/src/recursion.clj
index 95d77aa..79ce297 100644
--- a/src/recursion.clj
+++ b/src/recursion.clj
@@ -1,85 +1,225 @@
 (ns recursion)
 
+(defn my-sum [coll]
+  (if (empty? coll)
+    0
+    (+ (first coll) (my-sum (rest coll)))))
+
 (defn product [coll]
-  :-)
+  (if (empty? coll)
+    1
+    (* (first coll) (product (rest coll)))))
 
 (defn singleton? [coll]
-  :-)
+  (if (empty? coll)
+    false
+    (empty? (rest coll))))
 
 (defn my-last [coll]
-  :-)
+  (if (empty? coll)
+    nil
+    (if (singleton? coll)
+      (first coll)
+      (my-last (rest coll)))))
+
 
 (defn max-element [a-seq]
-  :-)
+  (if (empty? a-seq)
+    nil
+    (if (singleton? a-seq)
+      (first a-seq)
+      (max (first a-seq) (max-element (rest a-seq))))))
 
 (defn seq-max [seq-1 seq-2]
-  [:-])
+  (if (= (count seq-1) (count seq-2))
+    seq-2
+    (if (> (count seq-1) (count seq-2))
+      seq-1
+      seq-2)))
 
 (defn longest-sequence [a-seq]
-  [:-])
+  (if (empty? a-seq)
+    nil
+    (if (singleton? a-seq)
+      (first a-seq)
+      (seq-max (first a-seq) (longest-sequence (rest a-seq))))))
 
 (defn my-filter [pred? a-seq]
-  [:-])
+  (if (empty? a-seq)
+    ()
+    (if (pred? (first a-seq))
+      (cons (first a-seq) (my-filter pred? (rest a-seq)))
+      (my-filter pred? (rest a-seq)))))
+
 
 (defn sequence-contains? [elem a-seq]
-  :-)
+  (cond
+   (empty? a-seq)
+     false
+   (not (= elem (first a-seq)))
+      (sequence-contains? elem (rest a-seq))
+   :else
+      true))
 
 (defn my-take-while [pred? a-seq]
-  [:-])
+  (if (empty? a-seq)
+    ()
+    (if (pred? (first a-seq))
+      (cons (first a-seq) (my-take-while pred? (rest a-seq)))
+      ())))
 
 (defn my-drop-while [pred? a-seq]
-  [:-])
+  (if (empty? a-seq)
+    ()
+    (if (pred? (first a-seq))
+      (my-drop-while pred? (rest a-seq))
+      (seq a-seq))))
 
 (defn seq= [a-seq b-seq]
-  :-)
+  (cond
+   (not (= (count a-seq) (count b-seq)))
+     false
+   (and (empty? a-seq) (empty? b-seq))
+     true
+   (= (first a-seq) (first b-seq))
+     (seq= (rest a-seq) (rest b-seq))
+   :else
+     false))
 
 (defn my-map [f seq-1 seq-2]
-  [:-])
+  (if (and (empty? seq-2) (empty? seq-2))
+     ()
+     (cons (f (first seq-1) (first seq-2)) (my-map f (rest seq-1) (rest seq-2)))))
+
 
 (defn power [n k]
-  :-)
+  (cond
+   (zero? n)
+     0
+   (zero? k)
+     1
+   :else
+     (* n (power n (dec k)))))
+
+
+
 
 (defn fib [n]
-  :-)
+  (cond
+   (= n 0)
+     0
+   (= n 1)
+     1
+   :else
+    (+      (fib (- n 1))
+            (fib (- n 2)))))
 
 (defn my-repeat [how-many-times what-to-repeat]
-  [:-])
+  (cond
+   (= how-many-times -1)
+     ()
+   (= how-many-times 0)
+     ""
+   :else
+     (cons what-to-repeat (my-repeat (dec how-many-times) what-to-repeat))))
 
 (defn my-range [up-to]
-  [:-])
+  (cond
+   (= up-to 0)
+     ()
+   :else
+     (cons (dec up-to) (my-range (dec up-to)))))
 
 (defn tails [a-seq]
-  [:-])
+  (if (empty? a-seq)
+    (list ());list adds the last empty '()' in the result
+    (cons (seq a-seq) (tails (rest a-seq)))))
 
 (defn inits [a-seq]
-  [:-])
+  (if (empty? a-seq)
+    (list ())
+    (cons (seq a-seq) (inits (reverse (rest (reverse a-seq)))))))
 
 (defn rotations [a-seq]
-  [:-])
+  (if (empty? a-seq)
+    (list ())
+    (rest (map concat (tails a-seq) (reverse (inits a-seq))))))
+
 
 (defn my-frequencies-helper [freqs a-seq]
-  [:-])
+   (if (empty? a-seq)
+    freqs
+    (let [new-count (if (contains? freqs (first a-seq))
+                      (inc (get freqs (first a-seq)))
+                      1)]
+      (my-frequencies-helper (assoc freqs (first a-seq) new-count) (rest a-seq)))))
 
 (defn my-frequencies [a-seq]
-  [:-])
+  (if (empty? a-seq)
+    '{}
+    (my-frequencies-helper {} a-seq)))
+
+
+(defn un-frequencies-helper [a-seq a-map]
+  (if (empty? a-map)
+    a-seq
+    (un-frequencies-helper
+     (concat a-seq
+             (repeat (val (first a-map)) (key (first a-map))))
+             (rest a-map))))
+
+
 
 (defn un-frequencies [a-map]
-  [:-])
+  (if (empty? a-map)
+    ()
+    (un-frequencies-helper () a-map)))
 
 (defn my-take [n coll]
-  [:-])
+  (if (or (= n 0) (empty? coll))
+    ()
+    (cons (first coll) (my-take (dec n) (rest coll)))))
 
 (defn my-drop [n coll]
-  [:-])
+  (cond
+   (= n 0)
+    coll
+   (empty? coll)
+    ()
+   :else
+      (my-drop (dec n) (rest coll))))
 
 (defn halve [a-seq]
-  [:-])
+  (if (singleton? a-seq)
+    (vector () (list(first a-seq)))
+  (let [count_halve (int (/ (count a-seq) 2))]
+    (vector (my-take count_halve a-seq) (my-drop count_halve a-seq)))))
+
 
 (defn seq-merge [a-seq b-seq]
-  [:-])
+  (cond
+   (empty? a-seq)
+     b-seq
+   (empty? b-seq)
+     a-seq
+   :else
+     (if (< (first a-seq) (first b-seq))
+       ;a comes first, next round is rest a and full b
+       (cons (first a-seq) (seq-merge (rest a-seq) b-seq))
+       ;else: b comes first, next round is full a and rest b
+       (cons (first b-seq) (seq-merge a-seq (rest b-seq))))))
+
+
 
 (defn merge-sort [a-seq]
-  [:-])
+  (cond
+   (or (empty? a-seq) (singleton? a-seq))
+     a-seq
+   :else
+     (let [[first_half second_half] (halve a-seq)]
+       (seq-merge (merge-sort first_half) (merge-sort second_half)))))
+
+
 
 (defn split-into-monotonics [a-seq]
   [:-])