diff --git a/freq_freqs.txt b/freq_freqs.txt
new file mode 100644
index 0000000..0f4374e
--- /dev/null
+++ b/freq_freqs.txt
@@ -0,0 +1,12 @@
+1 32
+2 20
+3 10
+4 3
+5 1
+6 2
+7 1
+8 1
+9 1
+10 2
+12 1
+26 1
diff --git a/src/com/owoga/prhyme/corpus/db.clj b/src/com/owoga/prhyme/corpus/db.clj
index b63c25e..26ff7a9 100644
--- a/src/com/owoga/prhyme/corpus/db.clj
+++ b/src/com/owoga/prhyme/corpus/db.clj
@@ -1,2 +1,6 @@
 (ns com.owoga.prhyme.corpus.db
   (:require [integrant.core :as ig]))
+
+(defn tokens->db
+  [tokens]
+  )
diff --git a/src/com/owoga/prhyme/data/tpt.clj b/src/com/owoga/prhyme/data/tpt.clj
index b65a504..9cf7e4b 100644
--- a/src/com/owoga/prhyme/data/tpt.clj
+++ b/src/com/owoga/prhyme/data/tpt.clj
@@ -46,6 +46,37 @@
                        (bit-shift-left n 7))
                (inc i))))))
 
+(defn vb-decode
+  ([ba]
+   (vb-decode ba 0))
+  ([ba i]
+   (if (>= i (count ba))
+     (cons (first (vb-decode-1 ba))
+           nil)
+     (let [[value byte-count] (vb-decode-1 ba)]
+       (lazy-seq
+        (cons
+         value
+         (vb-decode (byte-array (drop byte-count ba))
+                    (+ i byte-count))))))))
+
+(comment
+  (let [n1 0
+        n2 1
+        n3 127
+        n4 128
+        n5 257
+        n6 9876543210
+        baos (java.io.ByteArrayOutputStream.)]
+    (->> [n1 n2 n3 n4 n5 n6]
+         (map vb-encode)
+         (run! #(.writeBytes baos %)))
+    (let [ba (.toByteArray baos)]
+      (vb-decode ba)))
+
+  ;; => ([0 1] [1 1] [127 1] [128 2] [257 2] [9876543210 5])
+  )
+
 (def dictionary ["hi" "my" "name" "is" "what"])
 
 (defn slurp-bytes [x]
diff --git a/src/com/owoga/prhyme/generation/simple_good_turing.clj b/src/com/owoga/prhyme/generation/simple_good_turing.clj
index 0381889..5276424 100644
--- a/src/com/owoga/prhyme/generation/simple_good_turing.clj
+++ b/src/com/owoga/prhyme/generation/simple_good_turing.clj
@@ -14,6 +14,10 @@
   commas, periods, and newlines."
   #"(?s).*?([a-zA-Z\d]+(?:['\-]?[a-zA-Z]+)?|,|\.|\n)")
 
+(defn pad-tokens
+  [tokens n]
+  (concat (repeat (min 1 (dec n)) "<s>") tokens ["</s>"]))
+
 (defn tokenize-line
   [line]
   (->> line
diff --git a/src/com/owoga/prhyme/rhyme_trie.clj b/src/com/owoga/prhyme/rhyme_trie.clj
new file mode 100644
index 0000000..51223d2
--- /dev/null
+++ b/src/com/owoga/prhyme/rhyme_trie.clj
@@ -0,0 +1,287 @@
+(ns com.owoga.prhyme.rhyme-trie
+  (:require [clojure.java.io :as io]
+            [clojure.walk :as walk]
+            [clojure.zip :as zip])
+  (:import (java.io ByteArrayOutputStream ByteArrayInputStream
+                    DataOutputStream DataInputStream)))
+
+(defn branch? [node]
+  (and (map? node)
+       (:children (first (vals node)))))
+
+(defn children [node]
+  (map (partial apply hash-map) (seq (:children (first (vals node))))))
+
+(defn without-children [node]
+  {(first (keys node))
+   (dissoc (get node (first (keys node))) :children)})
+
+(defn map-trie->seq-trie
+  [trie]
+  [(vec (map map-trie->seq-trie (children trie)))
+   (without-children trie)])
+
+(let [m {:root
+         {:children
+          {"T"
+           {:children
+            {"A" {:children
+                  {"T" {:value "TAT", :count 1}
+                   "S" {:value "SAT" :count 1}}
+                  :value "AT"
+                  :count 1},
+             "U" {:children {"T" {:value "TUT", :count 1}}}}}}}}]
+  (let [z (zip/vector-zip (map-trie->seq-trie m))]
+    (->> z
+         (iterate zip/next)
+         (take-while (complement zip/end?))
+         (map zip/node))))
+
+(defn vec-trie->map-trie
+  [trie]
+  (let [children (first trie)
+        parent (second trie)
+        [parent-key parent-val] (first (seq parent))]
+    {parent-key (assoc parent-val :children (into {} (map vec-trie->map-trie children)))}))
+
+(comment
+  (let [vect [[[[[[[[] {"T" {:value "TAT", :count 1}}]] {"A" {:value "AT", :count 1}}]
+                 [[[[] {"T" {:value "TUT", :count 1}}]] {"U" {}}]]
+                {"T" {}}]]
+              {:root {}}]]
+    (vec-trie->map-trie vect))
+
+  )
+
+(comment
+  (let [v1 '("T" "A" "T" "TAT")
+        v2 '("T" "U" "T" "TUT")
+        v3 '("T" "A" "AT")
+        t1 (trie v1)
+        t2 (trie v2)
+        t3 (trie v1 v2 v3)
+        vect (as-vec t3)]
+    vect)
+
+  )
+
+(defn parent?
+  [node]
+  (and (vector? (first node))
+       (map? (second node))))
+
+(defn child-seq [loc]
+  (if (and (zip/left loc)
+           (zip/down (zip/left loc)))
+    ((fn inner [child]
+       (if child
+         (lazy-seq
+          (cons child
+                (inner (zip/right child))))
+         nil))
+     (->> loc zip/left zip/down))
+    '()))
+
+(defn zip-visitor
+  ([visitor zipper]
+   (loop [zipper zipper]
+     (if(zip/end? zipper)
+       (zip/root zipper)
+       (recur (zip/next (visitor zipper)))))))
+
+(comment
+  (let [m {:root
+           {:children
+            {"T"
+             {:children
+              {"A" {:children
+                    {"T" {:value "TAT", :count 1}
+                     "S" {:value "SAT" :count 1}}
+                    :value "AT"
+                    :count 1},
+               "U" {:children {"T" {:value "TUT", :count 1}}}}}}}}]
+    (let [z (zip/vector-zip (map-trie->seq-trie m))
+          pred (fn [loc]
+                 (map? (zip/node loc)))]
+      (zip-visitor
+       (fn [loc]
+         (if (pred loc)
+           (zip/edit
+            loc
+            (fn [node]
+              (let [[k v] (first (seq node))
+                    children-counts (->> (child-seq loc)
+                                         (map zip/node)
+                                         (map (comp :count second first seq second)))]
+                (if (not-empty children-counts)
+                  (update-in node [k :count] (partial apply (fnil + 0)) children-counts)
+                  node))))
+           loc))
+       z)))
+
+  )
+
+(defprotocol ITrie
+  (as-map [this] "Map that underlies trie.")
+  (as-vec [this] "Depth-first post-order vector")
+  (transform [this f] "Depth-first post-order apply each function to each node."))
+
+;; Seq offers a depth-first post-order traversal
+;; with children ordered by key.
+(deftype Trie [trie]
+  ITrie
+  (as-map [_] trie)
+  (as-vec [_] (map-trie->seq-trie trie))
+  (transform [self f]
+    (->> self
+         as-vec
+         zip/vector-zip
+         (zip-visitor f)
+         (vec-trie->map-trie)
+         (Trie.)))
+
+  clojure.lang.IPersistentCollection
+  (seq [self]
+    (->> self
+         as-vec
+         zip/vector-zip
+         (iterate zip/next)
+         (take-while (complement zip/end?))
+         (map zip/node)
+         (filter map?)
+         (filter (comp :value second first seq))))
+  (cons [_ o]
+    (let [path (cons :root (interleave (repeat :children) (butlast o)))
+          id (last o)
+          node (get-in trie path)]
+      (Trie.
+       (update-in
+        trie
+        path
+        (fn [prev]
+          (if (nil? prev)
+            {:value id
+             :count 1}
+            (-> prev
+                (assoc :value id)       ; Assert value same?
+                (update :count (fnil inc 0)))))))))
+  (empty [_] (Trie. {}))
+  (equiv [_ o]
+    (and (isa? (class o) Trie)
+         (= (as-map o) trie))))
+
+(defn trie
+  ([] (->Trie {}))
+  ([& entries]
+   (reduce
+    (fn [t entry]
+      (conj t entry))
+    (trie)
+    entries)))
+
+(comment
+  (let [v1 '("T" "A" "T" "TAT")
+        v2 '("T" "U" "T" "TUT")
+        v3 '("T" "A" "AT")
+        t1 (trie v1)
+        t2 (trie v2)
+        t3 (trie v1 v2 v3)]
+    (seq t3))
+
+  (let [v1 '("T" "A" "T" "TAT")
+        v2 '("T" "U" "T" "TUT")
+        v3 '("T" "A" "AT")
+        t1 (trie v1)
+        t2 (trie v2)
+        t3 (trie v1 v2 v3)
+        pred (fn [loc]
+               (map? (zip/node loc)))]
+    (transform
+     t3
+     (fn [loc]
+       (if (pred loc)
+         (zip/edit
+          loc
+          (fn [node]
+            (let [[k v] (first (seq node))
+                  children-counts (->> (child-seq loc)
+                                       (map zip/node)
+                                       (map (comp :count second first seq second)))]
+              (if (not-empty children-counts)
+                (update-in node [k :count] (partial apply (fnil + 0)) children-counts)
+                node))))
+         loc))))
+
+  )
+
+(defn vec->trie
+  [v]
+  (let [zipper (zip/vector-zip v)]
+    (->> zipper
+         (iterate zip/next)
+         (take-while (complement zip/end?))
+         (filter (comp map? zip/node))
+         #_(map #(concat (zip/path %) [(->> % zip/node keys first)
+                                       (->> % zip/node vals first :value)]))
+         (map zip/path))))
+
+(comment
+  (let [v1 '("T" "A" "T" "TAT")
+        v2 '("T" "U" "T" "TUT")
+        v3 '("T" "A" "AT")
+        t1 (trie v1)
+        t2 (trie v2)
+        t3 (trie v1 v2 v3)
+        vect (as-vec t3)]
+    (vec->trie vect))
+
+  )
+
+
+(defn write-node [baos node])
+(defn write-index [baos children])
+
+(defn pack-index-to-children [children]
+  (let [baos (ByteArrayOutputStream.)]
+    (run!
+     (fn [[index-key byte-address]]
+       (.write baos index-key)
+       (.write baos byte-address))
+     children)
+    (.toByteArray baos)))
+
+(defn node->byte-array [index-key node-value children]
+  (let [baos (ByteArrayOutputStream.)
+        child-index (pack-index-to-children children)]
+    (.write baos node-value)
+    (.write baos (count child-index))
+    (.writeBytes baos child-index)
+    (.toByteArray baos)))
+
+
+(defn tpt [trie]
+  (let [node? (fn [x]
+                (and (seq? x)
+                     (not-empty x)
+                     (not (seq? (first x)))))
+        transform (fn [x]
+                    (if (node? x)
+                      (let [[index-key node-value children] x]
+                        (list index-key node-value (count children) children))
+                      x))]
+    (walk/postwalk transform trie)))
+
+
+(comment
+  (let [trie '(b 3 ())]
+    (tpt trie))
+
+  (let [trie '(nil 20 ((a 17 ())))]
+    (tpt trie))
+
+  (let [trie '(nil 20 ((a 17 ((a 10 ())
+                              (b 7 ())))
+                       (b 3 ())))]
+    (tpt trie))
+
+  )
diff --git a/test/com/owoga/prhyme/generation/simple_good_turing_test.clj b/test/com/owoga/prhyme/generation/simple_good_turing_test.clj
index 140f8ec..21817c7 100644
--- a/test/com/owoga/prhyme/generation/simple_good_turing_test.clj
+++ b/test/com/owoga/prhyme/generation/simple_good_turing_test.clj
@@ -12,6 +12,11 @@
   (with-open [reader (io/reader (io/resource "dark-corpus-test.txt"))]
     (->> (line-seq reader) doall)))
 
+(def test-sentence (first test-corpus))
+
+(def test-tokens
+  (sgt/pad-tokens (sgt/tokenize-line test-sentence) 1))
+
 (def train-trie
   (sgt/lines->trie train-corpus 3))
 
@@ -31,3 +36,49 @@
 (deftest simple-good-turing
   (testing "accuracy"))
 
+(partition 2 1 test-tokens)
+;; => (("<s>" "three")
+;;     ("three" "years")
+;;     ("years" "passed")
+;;     ("passed" "since")
+;;     ("since" "it")
+;;     ("it" "began")
+;;     ("began" "</s>"))
+
+(defn ngram-perplexity [model vocab n]
+  (fn [tokens]
+    (->> tokens
+         (partition n 1)
+         (map #(model vocab %))
+         (map #(/ (Math/log %)
+                  (Math/log 2))))))
+
+(def unigram-perplexity (ngram-perplexity sgt-model vocab 1))
+(def bigram-perplexity (ngram-perplexity sgt-model vocab 2))
+(unigram-perplexity ["<s>" "you're" "a" "dweller" "</s>"])
+;; => (-2.3988984034800693
+;;     -9.075314877722885
+;;     -4.843244892573044
+;;     -11.69197410313705
+;;     -2.3988984034800693)
+;; => -30.408330680393117
+(bigram-perplexity ["<s>" "you're" "a" "dweller" "</s>"])
+;; => (-8.228033550648288 -9.95473739539021 -10.916015756609784 -13.731947650675696)
+;; => -42.830734353323976
+(sgt-model vocab '("it" "began"))
+(->> test-corpus
+     (map sgt/tokenize-line)
+     (map #(sgt/pad-tokens % 1))
+     (map #(partition 2 1 %))
+     (map
+      (fn [tokens]
+        (map #(sgt-model vocab %) tokens)))
+     (take 10)
+     (map
+      (fn [tokens]
+        (map #(/ (Math/log %)
+                 (Math/log 2))
+             tokens))))
+
+(/ (Math/log 10)
+   (Math/log 2))