diff --git a/approx.ts b/approx.ts
index 18ac253..b027792 100644
--- a/approx.ts
+++ b/approx.ts
@@ -22,18 +22,6 @@ namespace Approx {
         return allPassed
     }
 
-    function areEquivalent(a: string[], b: string[]): boolean {
-        if (a.length != b.length) {
-            return false
-        }
-        for (let s of a) {
-            if (b.indexOf(s) == -1) {
-                return false
-            }
-        }
-        return true
-    }
-    
     function arrangements(): boolean {
         let test: TernaryStringSet
         let allPassed: boolean = true
diff --git a/balance.ts b/balance.ts
new file mode 100644
index 0000000..88b5c5d
--- /dev/null
+++ b/balance.ts
@@ -0,0 +1,73 @@
+namespace Balance {
+    export function run(): boolean {
+        let test: TernaryStringSet
+        let allPassed: boolean = true
+        
+        // balance() improves bad tree structure
+        test = new TernaryStringSet()
+        for (let s of ShortEnglishList.words) {
+            test.add(s)
+        }
+        const badDepth: number = test.stats.depth
+        test.balance()
+        const goodDepth: number = test.stats.depth
+        
+        if (!areEquivalent(ShortEnglishList.words, test.toArray())) {
+            game.splash("Balance test 1a failed.")
+            allPassed = false
+        }
+        if (goodDepth >= badDepth) {
+            game.splash(`Balance test 1b failed. Bad depth: ${badDepth}, good depth: ${goodDepth}.`)
+            allPassed = false
+        }
+        if (test.has("")) {
+            game.splash("Balance test 1c failed.")
+            allPassed = false
+        }
+
+        // balance() preserves contents
+        test = new TernaryStringSet()
+        const words: string[] = [
+            "",
+            "a",
+            "ape",
+            "aphid",
+            "aphids",
+            "bee",
+            "bees",
+            "cat",
+            "cats",
+        ]
+
+        // Add words in the worst possible order.
+        for (let s of words) {
+            test.add(s)
+        }
+        test.balance()
+        if (!areEquivalent(words, test.toArray())) {
+            game.splash("Balance test 2 failed.")
+            allPassed = false
+        }
+
+        // balance() of empty tree is safe.
+        test = new TernaryStringSet()
+        try {
+            test.balance()
+            if (test.size != 0) {
+                game.splash("Balance test 3b failed.")
+                allPassed = false
+            }
+            test.add("")
+            test.balance()
+            if (test.size != 1) {
+                game.splash("Balance test 3c failed.")
+                allPassed = false
+            }
+        } catch {
+            game.splash("Balance test 3a failed.")
+            allPassed = false
+        }
+        
+        return allPassed
+    }
+}
\ No newline at end of file
diff --git a/common.ts b/common.ts
new file mode 100644
index 0000000..a305127
--- /dev/null
+++ b/common.ts
@@ -0,0 +1,11 @@
+function areEquivalent(a: string[], b: string[]): boolean {
+    if (a.length != b.length) {
+        return false
+    }
+    for (let s of a) {
+        if (b.indexOf(s) == -1) {
+            return false
+        }
+    }
+    return true
+}
diff --git a/compact.ts b/compact.ts
new file mode 100644
index 0000000..9db7323
--- /dev/null
+++ b/compact.ts
@@ -0,0 +1,260 @@
+namespace Compact {
+    export function run(): boolean {
+        let test: TernaryStringSet
+        let allPassed: boolean = true
+
+        const compactWords: TernaryStringSet = new TernaryStringSet(ShortEnglishList.words)
+        compactWords.compact()
+
+        // Getter matches state.
+        test = new TernaryStringSet()
+        if (test.compacted) {
+            game.splash("Compact test 1a failed.")
+            allPassed = false
+        }
+        test.addAll(["add", "bad", "mad",])
+        test.compact()
+        if (!test.compacted) {
+            game.splash("Compact test 1b failed.")
+            allPassed = false
+        }
+
+        // Empty set
+        test = new TernaryStringSet()
+        test.compact()
+        if (test.stats.nodes != 0) {
+            game.splash("Compact test 2a failed.")
+            allPassed = false
+        }
+        test.add("")
+        test.compact()
+        if (test.stats.nodes != 0) {
+            game.splash("Compact test 2b failed.")
+            allPassed = false
+        }
+        if (!test.has("")) {
+            game.splash("Compact test 2c failed.")
+            allPassed = false
+        }
+
+        // Trivial compaction of tree with no duplicates.
+        // For compaction to have an effect,
+        // there must be strings with common suffixes.
+        test = new TernaryStringSet()
+        test.clear()
+        test.add("A")
+        test.compact()
+        if (test.stats.nodes != 1) {
+            game.splash("Compact test 3a failed.")
+            allPassed = false
+        }
+        test.add("B")
+        test.compact()
+        if (test.stats.nodes != 2) {
+            game.splash("Compact test 3b failed.")
+            allPassed = false
+        }
+        if (!test.has("A")) {
+            game.splash("Compact test 3c failed.")
+            allPassed = false
+        }
+        if (!test.has("B")) {
+            game.splash("Compact test 3d failed.")
+            allPassed = false
+        }
+
+        /**
+         * Basic suffix sharing.
+         * Here, we add strings with a common suffix, "ing,"
+         * but different prefixes. In the original tree,
+         * each string will have its own subtree for its "ing,"
+         * but in the compacted tree, they will share one subtree.
+         */
+        test = new TernaryStringSet()
+        test.clear()
+        test.addAll(["abcing", "defing", "ghiing", "jkling", "mnoing",])
+        const preCompactSize: number = test.stats.nodes
+        test.compact()
+        if (3 * (test.size - 1) != preCompactSize - test.stats.nodes) {
+            game.splash("Compact test 4 failed.")
+            allPassed = false
+        }
+
+        /**
+         * Non-trivial suffix sharing.
+         * A more complex example than the basic test.
+         * In this case, each string has a unique prefix, "a" -- "d."
+         * All have a common suffix, "ing,"
+         * but two share the suffix "_aing"
+         * and two share the suffix "_bing."
+         * Before compactio0n, there is a node for each letter
+         * of each string (6 chars * 4 strings) since there are
+         * no shared prefixes. After compaction, we expect a node each
+         * for the prefixes, three nodes for the shared "ing,"
+         * two nodes for the shared "_a," and two for the "_b"
+         * (4 + 3 + 2 + 2)
+         */
+        test = new TernaryStringSet()
+        const words: string[] = ["a_aing", "b_aing", "c_bing", "d_bing",]
+        test.addAll(words)
+        if (test.stats.nodes != 24) {
+            game.splash("Compact test 5a failed.")
+            allPassed = false
+        }
+        test.compact()
+        if (test.stats.nodes != 11) {
+            game.splash("Compact test 5b failed.")
+            allPassed = false
+        }
+
+        /**
+         * If we add "e_ai," this will add 4 nodes since the prefix "e"
+         * is unique and "ai" was previously infix, not a suffix!
+         */
+        test.add("e_ai")
+        test.compact()
+        if (test.stats.nodes != 15) {
+            game.splash("Compact test 5c failed.")
+            allPassed = false
+        }
+
+        /**
+         * Whereas if we add "fng," only one more node is needed
+         * (for the "f"), since the suffix "ng" is part of the
+         * existing "ing" subtree.
+         */
+        test.add("fng")
+        test.compact()
+        if (test.stats.nodes != 16) {
+            game.splash("Compact test 5d failed.")
+            allPassed = false
+        }
+
+        // Dictionary compaction.
+        test = compactWords
+        if (test.size != ShortEnglishList.words.length) {
+            game.splash("Compact test 6a failed.")
+            allPassed = false
+        }
+        /**
+         * Non-trivial compacted set should have fewer nodes.
+         * In fact, for our word list, it is leff than half as many nodes!
+         */
+        let wordSet: TernaryStringSet = new TernaryStringSet(ShortEnglishList.words)
+        // game.splash(`Loose nodes: ${wordSet.stats.nodes}, compact nodes: ${test.stats.nodes}`)
+        if (test.stats.nodes >= wordSet.stats.nodes) {
+            game.splash("Compact test 6b failed.")
+            allPassed = false
+        }
+        // But it should contain all of the same words.
+        for (let s of ShortEnglishList.words) {
+            if (!test.has(s)) {
+                game.splash(`Compact test 6c failed word ${s}.`)
+                allPassed = false
+            }
+        }
+
+        /**
+         * Automatic decompaction on mutation.
+         * Attempting to mutate a compact set must leave it uncompacted.
+         */
+        const compactOriginal: TernaryStringSet = new TernaryStringSet()
+        compactOriginal.addAll([
+            "alligator",
+            "bass",
+            "crane",
+            "dove",
+            "eagle",
+            "flea",
+            "porcupine",
+        ])
+        compactOriginal.compact()
+        if (!compactOriginal.compacted) {
+            game.splash("Compact test 7a failed.")
+            allPassed = false
+        }
+
+        // Copying a compact set yields a compact copy.
+        test = new TernaryStringSet(compactOriginal)
+        if (!test.compacted) {
+            game.splash("Compact test 7b failed.")
+            allPassed = false
+        }
+
+        // Adding a string already in the set has no effect.
+        test.add("alligator")
+        if (!test.compacted) {
+            game.splash("Compact test 7c failed.")
+            allPassed = false
+        }
+
+        // Adding a string not in the set undoes compaction.
+        test.add("dragonfly")
+        if (test.compacted) {
+            game.splash("Compact test 7d failed.")
+            allPassed = false
+        }
+
+        // As does adding via addAll().
+        test = new TernaryStringSet(compactOriginal)
+        test.addAll(["dragonfly",])
+        if (test.compacted) {
+            game.splash("Compact test 7e failed.")
+            allPassed = false
+        }
+
+        /**
+         * Likewise, deleting a string not in the set has no effect,
+         * while actually deleting a string undoes compaction.
+         */
+        test = new TernaryStringSet(compactOriginal)
+        test.delete("zedonk")
+        if (!test.compacted) {
+            game.splash("Compact test 7f failed.")
+            allPassed = false
+        }
+        test.delete("alligator")
+        if (test.compacted) {
+            game.splash("Compact test 7g failed.")
+            allPassed = false
+        }
+
+        // balance() undoes compaction.
+        test = new TernaryStringSet(compactOriginal)
+        test.balance()
+        if (test.compacted) {
+            game.splash("Compact test 7h failed.")
+            allPassed = false
+        }
+
+        // clear() trivially resets the compaction state.
+        test = new TernaryStringSet(compactOriginal)
+        test.clear()
+        if (test.compacted) {
+            game.splash("Compact test 7i failed.")
+            allPassed = false
+        }
+
+        // Non-mutating methods do not decompact.
+        const rhs: TernaryStringSet = new TernaryStringSet(["list", "wrestle",])
+        test = compactWords
+        // test.equals(rhs)
+        test.forEach((s) => s)
+        test.getArrangementsOf("coat")
+        test.getCompletionsOf("win")
+        test.getPartialMatchesOf("cu.")
+        test.getWithinHammingDistanceOf("cat", 1)
+        test.has("cat")
+        // test.isSubsetOf(rhs)
+        // test.isSupersetOf(rhs)
+        // test.keys
+        test.size
+        // test.values
+        if (!test.compacted) {
+            game.splash("Compact test 8 failed.")
+            allPassed = false
+        }
+
+        return allPassed
+    }
+}
\ No newline at end of file
diff --git a/main.ts b/main.ts
index 527316f..b2c35fc 100644
--- a/main.ts
+++ b/main.ts
@@ -32,6 +32,14 @@ if (!Approx.run()) {
     allPassed = false
 }
 
+if (!Balance.run()) {
+    allPassed = false
+}
+
+if (!Compact.run()) {
+    allPassed = false
+}
+
 // Show summary.
 if (allPassed) {
     game.splash("All tests passed!")
diff --git a/pxt.json b/pxt.json
index 4f7b4ad..6f7e9fa 100644
--- a/pxt.json
+++ b/pxt.json
@@ -3,7 +3,7 @@
     "version": "0.0.0",
     "dependencies": {
         "device": "*",
-        "pxt-fast-ternary-string-set": "github:robo-technical-group/pxt-fast-ternary-string-set#v1.7.1"
+        "pxt-fast-ternary-string-set": "github:robo-technical-group/pxt-fast-ternary-string-set#v1.9.0"
     },
     "files": [
         "main.ts",
@@ -14,7 +14,10 @@
         "size.ts",
         "delete.ts",
         "stats.ts",
-        "approx.ts"
+        "approx.ts",
+        "balance.ts",
+        "compact.ts",
+        "common.ts"
     ],
     "testDependencies": {},
     "targetVersions": {