diff --git a/lib/feed-v1/index.js b/lib/feed-v1/index.js
index bc63d7c..aebe136 100644
--- a/lib/feed-v1/index.js
+++ b/lib/feed-v1/index.js
@@ -5,6 +5,7 @@
 const stringify = require('fast-json-stable-stringify')
 const ed25519 = require('ssb-keys/sodium')
 const base58 = require('bs58')
+const union = require('set.prototype.union')
 const { stripAuthor } = require('./strip')
 const { getMsgId, getMsgHash } = require('./get-msg-id')
 const representContent = require('./represent-content')
@@ -15,6 +16,7 @@ const {
   validateBatch,
   validateMsgHash,
 } = require('./validation')
+const Tangle = require('../tangle')
 
 /**
  * @typedef {Iterator<Msg> & {values: () => Iterator<Msg>}} MsgIter
@@ -51,7 +53,7 @@ const {
  * @property {string} type
  * @property {number} when
  * @property {Keys} keys
- * @property {Record<string, MsgIter>} tangles
+ * @property {Record<string, Tangle>} tangles
  */
 
 /**
@@ -93,122 +95,6 @@ function toPlaintextBuffer(opts) {
   return Buffer.from(stringify(opts.content), 'utf8')
 }
 
-function calculateDepth(existing, tangleId = null) {
-  let max = -1
-  for (const msg of existing.values()) {
-    const depth = msg.metadata.tangles[tangleId]?.depth ?? 0
-    if (depth > max) {
-      max = depth
-    }
-  }
-  return max + 1
-}
-
-function lipmaa(n) {
-  let m = 1
-  let po3 = 3
-  let u = n
-
-  // find k such that (3^k - 1)/2 >= n
-  while (m < n) {
-    po3 *= 3
-    m = (po3 - 1) / 2
-  }
-
-  // find longest possible backjump
-  po3 /= 3
-  if (m !== n) {
-    while (u !== 0) {
-      m = (po3 - 1) / 2
-      po3 /= 3
-      u %= m
-    }
-
-    if (m !== po3) {
-      po3 = m
-    }
-  }
-
-  return n - po3
-}
-
-function determineTips(existing, tangleId = null) {
-  const tips = new Set()
-  for (const msg of existing.values()) {
-    tips.add(getMsgHash(msg))
-  }
-
-  for (const msg of existing.values()) {
-    const prev = msg.metadata.tangles[tangleId]?.prev ?? []
-    for (const p of prev) {
-      tips.delete(p)
-    }
-  }
-  return tips
-}
-
-function calculatePrev(existing, depth, lipmaaDepth, tangleId = null) {
-  const prev = []
-  const tips = determineTips(existing, tangleId)
-  for (const msg of existing.values()) {
-    const msgDepth = msg.metadata.tangles[tangleId]?.depth ?? 0
-    const msgHash = getMsgHash(msg)
-    if (
-      msgDepth === depth - 1 ||
-      msgDepth === lipmaaDepth ||
-      tips.has(msgHash)
-    ) {
-      prev.push(msgHash)
-    }
-  }
-  return prev
-}
-
-/**
- * @param {MsgIter} existing
- * @param {string} tangleId
- * @returns
- */
-function prevalidateExisting(existing, tangleId) {
-  if (!existing?.[Symbol.iterator]) {
-    // prettier-ignore
-    return new Error(`existing must be an iterator, but got ${typeof existing}`)
-  }
-  if (typeof existing?.values !== 'function') {
-    // prettier-ignore
-    return new Error(`existing must be a Map, Set, or Array, but got ${existing}`)
-  }
-  if (!tangleId) {
-    // prettier-ignore
-    return new Error(`tangleId must be a string, but got ${typeof tangleId}`)
-  }
-  let isEmpty = true
-  let hasDepthZeroMsg = false
-  for (const p of existing.values()) {
-    isEmpty = false
-    if (!p.metadata) {
-      // prettier-ignore
-      return new Error(`existing must contain messages, but got ${typeof p}`)
-    }
-
-    if (!p.metadata.tangles[tangleId] && getMsgHash(p) === tangleId) {
-      if (hasDepthZeroMsg) {
-        // prettier-ignore
-        return new Error(`existing must contain only 1 message with depth 0`)
-      } else {
-        hasDepthZeroMsg = true
-      }
-    } else if (!p.metadata.tangles[tangleId]) {
-      // prettier-ignore
-      return new Error(`existing must refer to the tangleId ${tangleId}`)
-    }
-  }
-  if (!isEmpty && !hasDepthZeroMsg) {
-    // prettier-ignore
-    return new Error(`opts.existing must contain the message with depth 0`)
-  }
-}
-
 /**
  * @param {CreateOpts} opts
  * @returns {Msg}
@@ -224,12 +110,11 @@ function create(opts) {
   if (opts.tangles) {
     for (const rootId in opts.tangles) {
       if ((err = validateMsgHash(rootId))) throw err
-      const existing = opts.tangles[rootId]
-      if ((err = prevalidateExisting(existing, rootId))) throw err
-
-      const depth = calculateDepth(existing, rootId)
-      const lipmaaDepth = lipmaa(depth + 1) - 1
-      const prev = calculatePrev(existing, depth, lipmaaDepth, rootId)
+      const tangle = opts.tangles[rootId]
+      const depth = tangle.getMaxDepth() + 1
+      const tips = tangle.getTips()
+      const lipmaaSet = tangle.getLipmaaSet(depth)
+      const prev = [...union(lipmaaSet, tips)]
       tangles[rootId] = { depth, prev }
     }
   } else {
diff --git a/lib/feed-v1/validation.js b/lib/feed-v1/validation.js
index ba02966..f6a9c6d 100644
--- a/lib/feed-v1/validation.js
+++ b/lib/feed-v1/validation.js
@@ -1,6 +1,7 @@
 const base58 = require('bs58')
 const ed25519 = require('ssb-keys/sodium')
 const stringify = require('fast-json-stable-stringify')
+const Tangle = require('../tangle')
 
 function validateShape(msg) {
   if (!msg || typeof msg !== 'object') {
@@ -73,13 +74,23 @@ function validateSignature(msg) {
   }
 }
 
-function validateTangle(msg, existingMsgs, tangleId) {
-  const tangle = msg.metadata.tangles[tangleId]
-  if (!tangle?.prev || !Array.isArray(tangle.prev)) {
+/**
+ *
+ * @param {any} msg
+ * @param {Tangle} tangle
+ * @param {*} tangleId
+ * @returns
+ */
+function validateTangle(msg, tangle, tangleId) {
+  if (!msg.metadata.tangles[tangleId]) {
+    return new Error('invalid message: must have metadata.tangles.' + tangleId)
+  }
+  const { depth, prev } = msg.metadata.tangles[tangleId]
+  if (!prev || !Array.isArray(prev)) {
     // prettier-ignore
     return new Error('invalid message: prev must be an array, on feed: ' + msg.metadata.who);
   }
-  for (const p of tangle.prev) {
+  for (const p of prev) {
     if (typeof p !== 'string') {
       // prettier-ignore
       return new Error('invalid message: prev must contain strings but found ' + p + ', on feed: ' + msg.metadata.who);
@@ -89,18 +100,13 @@ function validateTangle(msg, existingMsgs, tangleId) {
       return new Error('invalid message: prev must not contain URIs, on feed: ' + msg.metadata.who);
     }
 
-    if (!existingMsgs.has(p)) {
+    if (!tangle.has(p)) {
       // prettier-ignore
       return new Error('invalid message: prev ' + p + ' is not locally known, on feed: ' + msg.metadata.who);
     }
-    const existingMsg = existingMsgs.get(p)
+    const prevDepth = tangle.getDepth(p)
 
-    if (existingMsg.metadata.type !== msg.metadata.type) {
-      // prettier-ignore
-      return new Error('invalid message: prev ' + p + ' is not from the same type, on feed: ' + msg.metadata.who);
-    }
-    const existingDepth = existingMsg.metadata.tangles[tangleId]?.depth ?? 0
-    if (existingDepth >= tangle.depth) {
+    if (prevDepth >= depth) {
       // prettier-ignore
       return new Error('invalid message: depth of prev ' + p + ' is not lower, on feed: ' + msg.metadata.who);
     }
@@ -158,7 +164,7 @@ function validateContent(msg) {
 
 // FIXME: validateDepth should be +1 of the max of prev depth
 
-function validateSync(msg, existingMsgs, msgHash, rootHash) {
+function validateSync(msg, tangle, msgHash, rootHash) {
   let err
   if ((err = validateShape(msg))) return err
   if ((err = validateWho(msg))) return err
@@ -166,15 +172,15 @@ function validateSync(msg, existingMsgs, msgHash, rootHash) {
   if (msgHash === rootHash) {
     if ((err = validateTangleRoot(msg))) return err
   } else {
-    if ((err = validateTangle(msg, existingMsgs, rootHash))) return err
+    if ((err = validateTangle(msg, tangle, rootHash))) return err
   }
   if ((err = validateContent(msg))) return err
   if ((err = validateSignature(msg))) return err
 }
 
-function validate(msg, existingMsgs, msgHash, rootHash, cb) {
+function validate(msg, tangle, msgHash, rootHash, cb) {
   let err
-  if ((err = validateSync(msg, existingMsgs, msgHash, rootHash))) {
+  if ((err = validateSync(msg, tangle, msgHash, rootHash))) {
     return cb(err)
   }
   cb()
diff --git a/lib/plugin.js b/lib/plugin.js
index ee9a94a..dd3fc60 100644
--- a/lib/plugin.js
+++ b/lib/plugin.js
@@ -4,6 +4,7 @@ const AAOL = require('async-append-only-log')
 const promisify = require('promisify-4loc')
 const Obz = require('obz')
 const FeedV1 = require('./feed-v1')
+const Tangle = require('./tangle')
 const { ReadyGate, isEmptyObject } = require('./utils')
 const { decrypt } = require('./encryption')
 
@@ -149,10 +150,10 @@ exports.init = function initDB(peer, config) {
   function add(msg, tangleRootHash, cb) {
     // TODO: optimize this. This may be slow if you're adding many msgs in a
     // row, because it creates a new Map() each time.
-    const tangleMsgs = populateTangle(tangleRootHash)
+    const tangle = new Tangle(tangleRootHash, records())
 
     const msgHash = FeedV1.getMsgHash(msg)
-    FeedV1.validate(msg, tangleMsgs, msgHash, tangleRootHash, validationCB)
+    FeedV1.validate(msg, tangle, msgHash, tangleRootHash, validationCB)
 
     function validationCB(err) {
       // prettier-ignore
@@ -180,20 +181,10 @@ exports.init = function initDB(peer, config) {
     return null
   }
 
-  function populateTangle(tangleId) {
-    const map = new Map()
-    for (const rec of records()) {
-      if (rec.hash === tangleId || rec.msg.metadata.tangles?.[tangleId]) {
-        map.set(rec.hash, rec.msg)
-      }
-    }
-    return map
-  }
-
   function populateTangles(tangleIds) {
     const tangles = {}
     for (const tangleId of tangleIds) {
-      tangles[tangleId] ??= populateTangle(tangleId)
+      tangles[tangleId] ??= new Tangle(tangleId, records())
     }
     return tangles
   }
@@ -325,5 +316,8 @@ exports.init = function initDB(peer, config) {
 
     // internal
     findEncryptionFormatFor,
+
+    // mockable by tests
+    _getLog: () => log,
   }
 }
diff --git a/lib/tangle.js b/lib/tangle.js
index 88b299d..8e99b15 100644
--- a/lib/tangle.js
+++ b/lib/tangle.js
@@ -40,6 +40,11 @@ function compareMsgHashes(a, b) {
 }
 
 class Tangle {
+  /**
+   * @type {string}
+   */
+  #rootHash
+
   /**
    * @type {Set<string>}
    */
@@ -70,30 +75,34 @@ class Tangle {
    * @param {string} rootHash
    * @param {Iterable<Rec>} recordsIter
    */
-  constructor(rootHash, recordsIter) {
+  constructor(rootHash, recordsIter = []) {
+    this.#rootHash = rootHash
     this.#maxDepth = 0
     for (const rec of recordsIter) {
-      const msgHash = rec.hash
-      const tangles = rec.msg.metadata.tangles
-      if (msgHash === rootHash) {
-        this.#tips.add(msgHash)
-        this.#perDepth.set(0, [msgHash])
-        this.#depth.set(msgHash, 0)
-      } else if (tangles[rootHash]) {
-        this.#tips.add(msgHash)
-        const prev = tangles[rootHash].prev
-        for (const p of prev) {
-          this.#tips.delete(p)
-        }
-        this.#prev.set(msgHash, prev)
-        const depth = tangles[rootHash].depth
-        if (depth > this.#maxDepth) this.#maxDepth = depth
-        this.#depth.set(msgHash, depth)
-        const atDepth = this.#perDepth.get(depth) ?? []
-        atDepth.push(msgHash)
-        atDepth.sort(compareMsgHashes)
-        this.#perDepth.set(depth, atDepth)
+      this.add(rec.hash, rec.msg)
+    }
+  }
+
+  add(msgHash, msg) {
+    const tangles = msg.metadata.tangles
+    if (msgHash === this.#rootHash) {
+      this.#tips.add(msgHash)
+      this.#perDepth.set(0, [msgHash])
+      this.#depth.set(msgHash, 0)
+    } else if (tangles[this.#rootHash]) {
+      this.#tips.add(msgHash)
+      const prev = tangles[this.#rootHash].prev
+      for (const p of prev) {
+        this.#tips.delete(p)
       }
+      this.#prev.set(msgHash, prev)
+      const depth = tangles[this.#rootHash].depth
+      if (depth > this.#maxDepth) this.#maxDepth = depth
+      this.#depth.set(msgHash, depth)
+      const atDepth = this.#perDepth.get(depth) ?? []
+      atDepth.push(msgHash)
+      atDepth.sort(compareMsgHashes)
+      this.#perDepth.set(depth, atDepth)
     }
   }
 
diff --git a/package.json b/package.json
index 8c75815..a1c83b4 100644
--- a/package.json
+++ b/package.json
@@ -26,6 +26,7 @@
     "obz": "^1.1.0",
     "promisify-4loc": "^1.0.0",
     "push-stream": "^11.2.0",
+    "set.prototype.union": "^1.0.2",
     "ssb-uri2": "^2.4.1"
   },
   "devDependencies": {
@@ -44,7 +45,7 @@
     "tape": "^5.6.3"
   },
   "scripts": {
-    "test": "tape test/*.js | tap-arc --bail",
+    "test": "tape test/*.test.js | tap-arc --bail",
     "format-code": "prettier --write \"*.js\" \"(test|compat|indexes|operators)/*.js\"",
     "format-code-staged": "pretty-quick --staged --pattern \"*.js\" --pattern \"(test|compat|indexes|operators)/*.js\"",
     "coverage": "c8 --reporter=lcov npm run test"
diff --git a/test/add.test.js b/test/add.test.js
index fe8abf7..3857961 100644
--- a/test/add.test.js
+++ b/test/add.test.js
@@ -5,6 +5,7 @@ const rimraf = require('rimraf')
 const SecretStack = require('secret-stack')
 const caps = require('ssb-caps')
 const FeedV1 = require('../lib/feed-v1')
+const Tangle = require('../lib/tangle')
 const p = require('util').promisify
 const { generateKeypair } = require('./util')
 
@@ -32,7 +33,7 @@ test('add()', async (t) => {
     type: 'post',
     content: { text: 'This is the first post!' },
     tangles: {
-      [rootHash]: new Map([[FeedV1.getMsgHash(rootMsg), rootMsg]]),
+      [rootHash]: new Tangle(rootHash, [recRoot]),
     },
   })
 
diff --git a/test/create.test.js b/test/create.test.js
index 6a70c11..0043569 100644
--- a/test/create.test.js
+++ b/test/create.test.js
@@ -6,6 +6,7 @@ const SecretStack = require('secret-stack')
 const caps = require('ssb-caps')
 const p = require('util').promisify
 const FeedV1 = require('../lib/feed-v1')
+const Tangle = require('../lib/tangle')
 const { generateKeypair } = require('./util')
 
 const DIR = path.join(os.tmpdir(), 'ppppp-db-create')
@@ -72,9 +73,9 @@ test('add() forked then create() merged', async (t) => {
     type: 'post',
     content: { text: '3rd post forked from 1st' },
     tangles: {
-      [rootHash]: new Map([
-        [rootHash, rootMsg],
-        [rec1.hash, rec1.msg],
+      [rootHash]: new Tangle(rootHash, [
+        { hash: rootHash, msg: rootMsg },
+        rec1,
       ]),
     },
   })
diff --git a/test/feed-v1-create.test.js b/test/feed-v1-create.test.js
index a666b6d..52be52c 100644
--- a/test/feed-v1-create.test.js
+++ b/test/feed-v1-create.test.js
@@ -1,5 +1,6 @@
 const tape = require('tape')
 const FeedV1 = require('../lib/feed-v1')
+const Tangle = require('../lib/tangle')
 const { generateKeypair } = require('./util')
 
 let rootMsg = null
@@ -30,7 +31,7 @@ tape('FeedV1.create()', (t) => {
     content,
     type: 'post',
     tangles: {
-      [rootHash]: new Map([[rootHash, rootMsg]]),
+      [rootHash]: new Tangle(rootHash, [{ hash: rootHash, msg: rootMsg }]),
     },
     when,
   })
@@ -71,9 +72,9 @@ tape('FeedV1.create()', (t) => {
     content: content2,
     type: 'post',
     tangles: {
-      [rootHash]: new Map([
-        [rootHash, rootMsg],
-        [msgHash1, msg1],
+      [rootHash]: new Tangle(rootHash, [
+        { hash: rootHash, msg: rootMsg },
+        { hash: msgHash1, msg: msg1 },
       ]),
     },
     when: when + 1,
@@ -111,14 +112,14 @@ tape('FeedV1.create()', (t) => {
 tape('create() handles DAG tips correctly', (t) => {
   const keys = generateKeypair('alice')
   const when = 1652037377204
-  const existing = new Map([[rootHash, rootMsg]])
+  const tangle = new Tangle(rootHash, [{ hash: rootHash, msg: rootMsg }])
 
   const msg1 = FeedV1.create({
     keys,
     content: { text: '1' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: when + 1,
   })
@@ -129,14 +130,14 @@ tape('create() handles DAG tips correctly', (t) => {
     'msg1.prev is root'
   )
 
-  existing.set(msgHash1, msg1)
+  tangle.add(msgHash1, msg1)
 
   const msg2A = FeedV1.create({
     keys,
     content: { text: '2A' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: when + 2,
   })
@@ -151,9 +152,8 @@ tape('create() handles DAG tips correctly', (t) => {
     content: { text: '2B' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
-    existing,
     when: when + 2,
   })
   const msgHash2B = FeedV1.getMsgHash(msg2B)
@@ -163,14 +163,14 @@ tape('create() handles DAG tips correctly', (t) => {
     'msg2B.prev is msg1'
   )
 
-  existing.set(msgHash2B, msg2B)
+  tangle.add(msgHash2B, msg2B)
 
   const msg3 = FeedV1.create({
     keys,
     content: { text: '3' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: when + 3,
   })
@@ -180,10 +180,10 @@ tape('create() handles DAG tips correctly', (t) => {
     [rootHash, msgHash2B],
     'msg3.prev is root(lipmaa),msg2B(previous)'
   )
-  existing.set(msgHash3, msg3)
+  tangle.add(msgHash3, msg3)
 
   const msgHash2A = FeedV1.getMsgHash(msg2A)
-  existing.set(msgHash2A, msg2A)
+  tangle.add(msgHash2A, msg2A)
   t.pass('msg2A comes into awareness')
 
   const msg4 = FeedV1.create({
@@ -191,7 +191,7 @@ tape('create() handles DAG tips correctly', (t) => {
     content: { text: '4' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: when + 4,
   })
diff --git a/test/feed-v1-invalid-prev.test.js b/test/feed-v1-invalid-prev.test.js
index 7edeaa5..d72860e 100644
--- a/test/feed-v1-invalid-prev.test.js
+++ b/test/feed-v1-invalid-prev.test.js
@@ -1,6 +1,7 @@
 const tape = require('tape')
 const base58 = require('bs58')
 const FeedV1 = require('../lib/feed-v1')
+const Tangle = require('../lib/tangle')
 const { generateKeypair } = require('./util')
 
 tape('invalid msg with non-array prev', (t) => {
@@ -9,21 +10,21 @@ tape('invalid msg with non-array prev', (t) => {
   const rootMsg = FeedV1.createRoot(keys, 'post')
   const rootHash = FeedV1.getMsgHash(rootMsg)
 
-  const existing = new Map([[rootHash, rootMsg]])
+  const tangle = new Tangle(rootHash, [{ hash: rootHash, msg: rootMsg }])
 
   const msg = FeedV1.create({
     keys,
     content: { text: 'Hello world!' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: 1652030001000,
   })
   msg.metadata.tangles[rootHash].prev = null
   const msgHash = FeedV1.getMsgHash(msg)
 
-  FeedV1.validate(msg, existing, msgHash, rootHash, (err) => {
+  FeedV1.validate(msg, tangle, msgHash, rootHash, (err) => {
     t.ok(err, 'invalid 2nd msg throws')
     t.match(err.message, /prev must be an array/, 'invalid 2nd msg description')
     t.end()
@@ -36,26 +37,26 @@ tape('invalid msg with bad prev', (t) => {
   const rootMsg = FeedV1.createRoot(keys, 'post')
   const rootHash = FeedV1.getMsgHash(rootMsg)
 
-  const existing = new Map([[rootHash, rootMsg]])
+  const tangle = new Tangle(rootHash, [{ hash: rootHash, msg: rootMsg }])
 
   const msg1 = FeedV1.create({
     keys,
     content: { text: 'Hello world!' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: 1652030001000,
   })
   const msgHash1 = FeedV1.getMsgHash(msg1)
-  existing.set(msgHash1, msg1)
+  tangle.add(msgHash1, msg1)
 
   const msg2 = FeedV1.create({
     keys,
     content: { text: 'Hello world!' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: 1652030002000,
   })
@@ -63,7 +64,7 @@ tape('invalid msg with bad prev', (t) => {
   msg2.metadata.tangles[rootHash].prev = [1234]
   const msgHash2 = FeedV1.getMsgHash(msg2)
 
-  FeedV1.validate(msg2, existing, msgHash2, rootHash, (err) => {
+  FeedV1.validate(msg2, tangle, msgHash2, rootHash, (err) => {
     t.ok(err, 'invalid 2nd msg throws')
     t.match(
       err.message,
@@ -80,26 +81,26 @@ tape('invalid msg with URI in prev', (t) => {
   const rootMsg = FeedV1.createRoot(keys, 'post')
   const rootHash = FeedV1.getMsgHash(rootMsg)
 
-  const existing = new Map([[rootHash, rootMsg]])
+  const tangle = new Tangle(rootHash, [{ hash: rootHash, msg: rootMsg }])
 
   const msg1 = FeedV1.create({
     keys,
     content: { text: 'Hello world!' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: 1652030001000,
   })
   const msgHash1 = FeedV1.getMsgHash(msg1)
-  existing.set(msgHash1, msg1)
+  tangle.add(msgHash1, msg1)
 
   const msg2 = FeedV1.create({
     keys,
     content: { text: 'Hello world!' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: 1652030002000,
   })
@@ -109,7 +110,7 @@ tape('invalid msg with URI in prev', (t) => {
   msg2.metadata.tangles[rootHash].depth = 1
   msg2.metadata.tangles[rootHash].prev = [fakeMsgKey1]
 
-  FeedV1.validate(msg2, existing, msgHash2, rootHash, (err) => {
+  FeedV1.validate(msg2, tangle, msgHash2, rootHash, (err) => {
     t.ok(err, 'invalid 2nd msg throws')
     t.match(
       err.message,
@@ -126,26 +127,26 @@ tape('invalid msg with unknown prev', (t) => {
   const rootMsg = FeedV1.createRoot(keys, 'post')
   const rootHash = FeedV1.getMsgHash(rootMsg)
 
-  const existing = new Map([[rootHash, rootMsg]])
+  const tangle = new Tangle(rootHash, [{ hash: rootHash, msg: rootMsg }])
 
   const msg1 = FeedV1.create({
     keys,
     content: { text: 'Hello world!' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: 1652030001000,
   })
   const msgHash1 = FeedV1.getMsgHash(msg1)
-  existing.set(msgHash1, msg1)
+  tangle.add(msgHash1, msg1)
 
   const unknownMsg = FeedV1.create({
     keys,
     content: { text: 'Alien' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: 1652030001000,
   })
@@ -156,13 +157,16 @@ tape('invalid msg with unknown prev', (t) => {
     content: { text: 'Hello world!' },
     type: 'post',
     tangles: {
-      [rootHash]: new Map([[rootHash, rootMsg], [unknownMsgHash, unknownMsg]]),
+      [rootHash]: new Tangle(rootHash, [
+        { hash: rootHash, msg: rootMsg },
+        { hash: unknownMsgHash, msg: unknownMsg },
+      ]),
     },
     when: 1652030002000,
   })
   const msgHash2 = FeedV1.getMsgHash(msg2)
 
-  FeedV1.validate(msg2, existing, msgHash2, rootHash, (err) => {
+  FeedV1.validate(msg2, tangle, msgHash2, rootHash, (err) => {
     t.ok(err, 'invalid 2nd msg throws')
     t.match(
       err.message,
diff --git a/test/feed-v1-lipmaa.test.js b/test/feed-v1-lipmaa.test.js
index 2e7c01c..9057b98 100644
--- a/test/feed-v1-lipmaa.test.js
+++ b/test/feed-v1-lipmaa.test.js
@@ -1,28 +1,28 @@
 const tape = require('tape')
 const FeedV1 = require('../lib/feed-v1')
+const Tangle = require('../lib/tangle')
 const { generateKeypair } = require('./util')
 
 tape('lipmaa prevs', (t) => {
   const keys = generateKeypair('alice')
   const content = { text: 'Hello world!' }
   const when = 1652037377204
-  const existing = new Map()
 
   const rootMsg = FeedV1.createRoot(keys, 'post')
   const rootHash = FeedV1.getMsgHash(rootMsg)
-  existing.set(rootHash, rootMsg)
+  const tangle = new Tangle(rootHash, [{ hash: rootHash, msg: rootMsg }])
 
   const msg1 = FeedV1.create({
     keys,
     content,
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: when + 1,
   })
   const msgHash1 = FeedV1.getMsgHash(msg1)
-  existing.set(msgHash1, msg1)
+  tangle.add(msgHash1, msg1)
   t.equals(msg1.metadata.tangles[rootHash].depth, 1, 'msg1 depth')
   t.deepEquals(msg1.metadata.tangles[rootHash].prev, [rootHash], 'msg1 prev')
 
@@ -31,30 +31,26 @@ tape('lipmaa prevs', (t) => {
     content,
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: when + 2,
   })
   const msgHash2 = FeedV1.getMsgHash(msg2)
-  existing.set(msgHash2, msg2)
+  tangle.add(msgHash2, msg2)
   t.equals(msg2.metadata.tangles[rootHash].depth, 2, 'msg2 depth')
-  t.deepEquals(
-    msg2.metadata.tangles[rootHash].prev,
-    [msgHash1],
-    'msg2 prev'
-  )
+  t.deepEquals(msg2.metadata.tangles[rootHash].prev, [msgHash1], 'msg2 prev')
 
   const msg3 = FeedV1.create({
     keys,
     content,
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: when + 3,
   })
   const msgHash3 = FeedV1.getMsgHash(msg3)
-  existing.set(msgHash3, msg3)
+  tangle.add(msgHash3, msg3)
   t.equals(msg3.metadata.tangles[rootHash].depth, 3, 'msg3 depth')
   t.deepEquals(
     msg3.metadata.tangles[rootHash].prev,
@@ -67,66 +63,54 @@ tape('lipmaa prevs', (t) => {
     content,
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: when + 4,
   })
   const msgHash4 = FeedV1.getMsgHash(msg4)
-  existing.set(msgHash4, msg4)
+  tangle.add(msgHash4, msg4)
   t.equals(msg4.metadata.tangles[rootHash].depth, 4, 'msg4 depth')
-  t.deepEquals(
-    msg4.metadata.tangles[rootHash].prev,
-    [msgHash3],
-    'msg4 prev'
-  )
+  t.deepEquals(msg4.metadata.tangles[rootHash].prev, [msgHash3], 'msg4 prev')
 
   const msg5 = FeedV1.create({
     keys,
     content,
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: when + 5,
   })
   const msgHash5 = FeedV1.getMsgHash(msg5)
-  existing.set(msgHash5, msg5)
+  tangle.add(msgHash5, msg5)
   t.equals(msg5.metadata.tangles[rootHash].depth, 5, 'msg5 depth')
-  t.deepEquals(
-    msg5.metadata.tangles[rootHash].prev,
-    [msgHash4],
-    'msg5 prev'
-  )
+  t.deepEquals(msg5.metadata.tangles[rootHash].prev, [msgHash4], 'msg5 prev')
 
   const msg6 = FeedV1.create({
     keys,
     content,
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: when + 6,
   })
   const msgHash6 = FeedV1.getMsgHash(msg6)
-  existing.set(msgHash6, msg6)
+  tangle.add(msgHash6, msg6)
   t.equals(msg6.metadata.tangles[rootHash].depth, 6, 'msg6 depth')
-  t.deepEquals(
-    msg6.metadata.tangles[rootHash].prev,
-    [msgHash5],
-    'msg6 prev'
-  )
+  t.deepEquals(msg6.metadata.tangles[rootHash].prev, [msgHash5], 'msg6 prev')
 
   const msg7 = FeedV1.create({
     keys,
     content,
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: when + 7,
   })
   const msgHash7 = FeedV1.getMsgHash(msg7)
-  existing.set(msgHash7, msg7)
+  tangle.add(msgHash7, msg7)
   t.equals(msg7.metadata.tangles[rootHash].depth, 7, 'msg7 depth')
   t.deepEquals(
     msg7.metadata.tangles[rootHash].prev,
@@ -134,6 +118,5 @@ tape('lipmaa prevs', (t) => {
     'msg7 prev (has lipmaa!)'
   )
 
-
   t.end()
 })
diff --git a/test/feed-v1-tangles.test.js b/test/feed-v1-tangles.test.js
index 66b6d5a..8d832eb 100644
--- a/test/feed-v1-tangles.test.js
+++ b/test/feed-v1-tangles.test.js
@@ -1,27 +1,26 @@
 const tape = require('tape')
 const FeedV1 = require('../lib/feed-v1')
+const Tangle = require('../lib/tangle')
 const { generateKeypair } = require('./util')
 
 tape('simple multi-author tangle', (t) => {
   const keysA = generateKeypair('alice')
   const keysB = generateKeypair('bob')
-  const existingA = new Map()
-  const existingB = new Map()
 
   const rootMsgA = FeedV1.createRoot(keysA, 'post')
   const rootHashA = FeedV1.getMsgHash(rootMsgA)
-  existingA.set(rootHashA, rootMsgA)
+  const tangleA = new Tangle(rootHashA, [{ hash: rootHashA, msg: rootMsgA }])
 
   const rootMsgB = FeedV1.createRoot(keysB, 'post')
   const rootHashB = FeedV1.getMsgHash(rootMsgB)
-  existingB.set(rootHashB, rootMsgB)
+  const tangleB = new Tangle(rootHashB, [{ hash: rootHashB, msg: rootMsgB }])
 
   const msg1 = FeedV1.create({
     keys: keysA,
     content: { text: 'Hello world!' },
     type: 'post',
     tangles: {
-      [rootHashA]: existingA,
+      [rootHashA]: tangleA,
     },
     when: 1652030001000,
   })
@@ -36,10 +35,9 @@ tape('simple multi-author tangle', (t) => {
     keys: keysB,
     content: { text: 'Hello world!' },
     type: 'post',
-    existing: new Map(),
     tangles: {
-      [rootHashB]: existingB,
-      [msgHash1]: new Map([[msgHash1, msg1]]),
+      [rootHashB]: tangleB,
+      [msgHash1]: new Tangle(msgHash1, [{ hash: msgHash1, msg: msg1 }]),
     },
     when: 1652030002000,
   })
@@ -72,48 +70,47 @@ tape('lipmaa in multi-author tangle', (t) => {
 
   const content = { text: 'Hello world!' }
   const when = 1652037377204
-  const existingA = new Map()
-  const existingB = new Map()
-  const tangleExisting = new Map()
 
   const rootMsgA = FeedV1.createRoot(keysA, 'post')
   const rootHashA = FeedV1.getMsgHash(rootMsgA)
-  existingA.set(rootHashA, rootMsgA)
+  const tangleA = new Tangle(rootHashA, [{ hash: rootHashA, msg: rootMsgA }])
 
   const rootMsgB = FeedV1.createRoot(keysB, 'post')
   const rootHashB = FeedV1.getMsgHash(rootMsgB)
-  existingB.set(rootHashB, rootMsgB)
-
+  const tangleB = new Tangle(rootHashB, [{ hash: rootHashB, msg: rootMsgB }])
 
   const msg1 = FeedV1.create({
     keys: keysA,
     content,
     type: 'post',
     tangles: {
-      [rootHashA]: existingA,
+      [rootHashA]: tangleA,
     },
     when: when + 1,
   })
   const msgHash1 = FeedV1.getMsgHash(msg1)
-  existingA.set(msgHash1, msg1)
-  tangleExisting.set(msgHash1, msg1)
+  tangleA.add(msgHash1, msg1)
+  const tangleThread = new Tangle(msgHash1, [{ hash: msgHash1, msg: msg1 }])
 
-  t.deepEquals(Object.keys(msg1.metadata.tangles),[rootHashA], 'A:msg1 has only feed tangle')
+  t.deepEquals(
+    Object.keys(msg1.metadata.tangles),
+    [rootHashA],
+    'A:msg1 has only feed tangle'
+  )
 
   const msg2 = FeedV1.create({
     keys: keysB,
     content,
     type: 'post',
-    existing: existingB,
     tangles: {
-      [rootHashB]: existingB,
-      [msgHash1]: tangleExisting,
+      [rootHashB]: tangleB,
+      [msgHash1]: tangleThread,
     },
     when: when + 2,
   })
   const msgHash2 = FeedV1.getMsgHash(msg2)
-  existingB.set(msgHash2, msg2)
-  tangleExisting.set(msgHash2, msg2)
+  tangleB.add(msgHash2, msg2)
+  tangleThread.add(msgHash2, msg2)
 
   t.deepEquals(
     msg2.metadata.tangles[msgHash1].prev,
@@ -125,16 +122,15 @@ tape('lipmaa in multi-author tangle', (t) => {
     keys: keysB,
     content,
     type: 'post',
-    existing: existingB,
     tangles: {
-      [rootHashB]: existingB,
-      [msgHash1]: tangleExisting,
+      [rootHashB]: tangleB,
+      [msgHash1]: tangleThread,
     },
     when: when + 3,
   })
   const msgHash3 = FeedV1.getMsgHash(msg3)
-  existingB.set(msgHash3, msg3)
-  tangleExisting.set(msgHash3, msg3)
+  tangleB.add(msgHash3, msg3)
+  tangleThread.add(msgHash3, msg3)
 
   t.deepEquals(
     msg3.metadata.tangles[msgHash1].prev,
@@ -146,16 +142,15 @@ tape('lipmaa in multi-author tangle', (t) => {
     keys: keysA,
     content,
     type: 'post',
-    existing: existingA,
     tangles: {
-      [rootHashA]: existingA,
-      [msgHash1]: tangleExisting,
+      [rootHashA]: tangleA,
+      [msgHash1]: tangleThread,
     },
     when: when + 4,
   })
   const msgHash4 = FeedV1.getMsgHash(msg4)
-  existingB.set(msgHash4, msg4)
-  tangleExisting.set(msgHash4, msg4)
+  tangleB.add(msgHash4, msg4)
+  tangleThread.add(msgHash4, msg4)
 
   t.deepEquals(
     msg4.metadata.tangles[msgHash1].prev,
diff --git a/test/feed-v1-validate.test.js b/test/feed-v1-validate.test.js
index 07d4358..0916f2e 100644
--- a/test/feed-v1-validate.test.js
+++ b/test/feed-v1-validate.test.js
@@ -1,17 +1,17 @@
 const tape = require('tape')
 const base58 = require('bs58')
 const FeedV1 = require('../lib/feed-v1')
+const Tangle = require('../lib/tangle')
 const { generateKeypair } = require('./util')
 
 tape('validate root msg', (t) => {
   const keys = generateKeypair('alice')
-  const existing = new Map()
 
   const rootMsg = FeedV1.createRoot(keys, 'post')
   const rootHash = FeedV1.getMsgHash(rootMsg)
-  existing.set(rootHash, rootMsg)
+  const tangle = new Tangle(rootHash, [{ hash: rootHash, msg: rootMsg }])
 
-  FeedV1.validate(rootMsg, existing, rootHash, rootHash, (err) => {
+  FeedV1.validate(rootMsg, tangle, rootHash, rootHash, (err) => {
     if (err) console.log(err)
     t.error(err, 'valid root msg')
     t.end()
@@ -20,25 +20,24 @@ tape('validate root msg', (t) => {
 
 tape('validate 2nd msg with existing root', (t) => {
   const keys = generateKeypair('alice')
-  const existing = new Map()
 
   const rootMsg = FeedV1.createRoot(keys, 'post')
   const rootHash = FeedV1.getMsgHash(rootMsg)
-  existing.set(rootHash, rootMsg)
+  const tangle = new Tangle(rootHash, [{ hash: rootHash, msg: rootMsg }])
 
   const msg1 = FeedV1.create({
     keys,
     content: { text: 'Hello world!' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: 1652030001000,
   })
   const msgHash1 = FeedV1.getMsgHash(msg1)
-  existing.set(msgHash1, msg1)
+  tangle.add(msgHash1, msg1)
 
-  FeedV1.validate(msg1, existing, msgHash1, rootHash, (err) => {
+  FeedV1.validate(msg1, tangle, msgHash1, rootHash, (err) => {
     if (err) console.log(err)
     t.error(err, 'valid 2nd msg')
     t.end()
@@ -48,18 +47,16 @@ tape('validate 2nd msg with existing root', (t) => {
 tape('validate 2nd forked msg', (t) => {
   const keys = generateKeypair('alice')
 
-  const existing = new Map()
-
   const rootMsg = FeedV1.createRoot(keys, 'post')
   const rootHash = FeedV1.getMsgHash(rootMsg)
-  existing.set(rootHash, rootMsg)
+  const tangle = new Tangle(rootHash, [{ hash: rootHash, msg: rootMsg }])
 
   const msg1A = FeedV1.create({
     keys,
     content: { text: 'Hello world!' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     existing: new Map(),
     when: 1652030001000,
@@ -71,15 +68,15 @@ tape('validate 2nd forked msg', (t) => {
     content: { text: 'Hello world!' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: 1652030002000,
   })
   const msgHash1B = FeedV1.getMsgHash(msg1B)
 
-  existing.set(msgHash1A, msg1A)
-  existing.set(msgHash1B, msg1B)
-  FeedV1.validate(msg1B, existing, msgHash1B, rootHash, (err) => {
+  tangle.add(msgHash1A, msg1A)
+  tangle.add(msgHash1B, msg1B)
+  FeedV1.validate(msg1B, tangle, msgHash1B, rootHash, (err) => {
     if (err) console.log(err)
     t.error(err, 'valid 2nd forked msg')
     t.end()
@@ -89,18 +86,16 @@ tape('validate 2nd forked msg', (t) => {
 tape('invalid msg with unknown previous', (t) => {
   const keys = generateKeypair('alice')
 
-  const existing = new Map()
-
   const rootMsg = FeedV1.createRoot(keys, 'post')
   const rootHash = FeedV1.getMsgHash(rootMsg)
-  existing.set(rootHash, rootMsg)
+  const tangle = new Tangle(rootHash, [{ hash: rootHash, msg: rootMsg }])
 
   const msg1 = FeedV1.create({
     keys,
     content: { text: 'Hello world!' },
     type: 'post',
     tangles: {
-      [rootHash]: existing,
+      [rootHash]: tangle,
     },
     when: 1652030001000,
   })
@@ -110,7 +105,7 @@ tape('invalid msg with unknown previous', (t) => {
 
   msg1.metadata.tangles[rootHash].prev = [fakeMsgHash]
 
-  FeedV1.validate(msg1, existing, msgHash1, rootHash, (err) => {
+  FeedV1.validate(msg1, tangle, msgHash1, rootHash, (err) => {
     t.ok(err, 'invalid 2nd msg throws')
     t.match(
       err.message,