diff --git a/avl.js b/avl.js
new file mode 100644
index 0000000..37315f7
--- /dev/null
+++ b/avl.js
@@ -0,0 +1,162 @@
+Array.prototype.equals = function(other) {
+    if (this.length != other.length) {
+        return false;
+    }
+
+    let i = this.length;
+    while (--i >= 0) {
+        if (this[i] !== other[i]) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+function balanceFactor(node) {
+    if (!node) {
+        return 0;
+    }
+
+    let [left, right] = [nodeRank(node.left), nodeRank(node.right)];
+    return right - left;
+}
+
+function updateRank(node) {
+    let [left, right] = [nodeRank(node.left), nodeRank(node.right)];
+    node.rank = 1 + Math.max(left, right);
+}
+
+class AVLTree extends RankedTree {
+    isCorrectNode(node, recursive) {
+        if (!node) {
+            return true;
+        }
+
+        recursive = recursive ?? true;
+
+        // FIXME: not enough, must be checked against differences
+        // let bf = balanceFactor(node);
+        // if (bf < -1 || bf > 1) {
+        //     return false;
+        // }
+
+        let differences = nodeDifferences(node);
+        differences.sort();
+        if (!differences.equals([1, 1]) && !differences.equals([1, 2])) {
+            return false;
+        }
+
+        return !recursive || (this.isCorrectNode(node.left) && this.isCorrectNode(node.right));
+    }
+
+    fix0Child(x, y, z, rotateLeft, rotateRight) {
+        let newRoot = x.parent;
+
+        if (!y || nodeDifference(y) == 2) {
+            newRoot = rotateRight(z);
+            z.demote();
+        } else if (nodeDifference(y) == 1) {
+            rotateLeft(x);
+            newRoot = rotateRight(z);
+
+            y.promote();
+            x.demote();
+            z.demote();
+        }
+
+        return newRoot;
+    }
+
+    insertRebalance(x) {
+        let diffs = nodeDifferences(x.parent).sort();
+        while (x.parent && diffs.equals([0, 1])) {
+            x.parent.promote();
+            x = x.parent;
+
+            diffs = nodeDifferences(x.parent).sort();
+        }
+
+        if (!x.parent) {
+            return;
+        }
+
+        let rotatingAroundRoot = x.parent.parent == null;
+        let newRoot = x.parent;
+
+        let rankDifference = nodeDifference(x);
+        if (rankDifference != 0) {
+            return;
+        }
+
+        let xParent = x.parent;
+
+        if (rankDifference == 0 && x.parent.left === x) {
+            newRoot = this.fix0Child(
+                x, x.right, xParent, rotateLeft, rotateRight
+            );
+        } else if (rankDifference == 0 && x.parent.right === x) {
+            newRoot = this.fix0Child(
+                x, x.left, xParent, rotateRight, rotateLeft
+            );
+        }
+
+        if (rotatingAroundRoot) {
+            this.root = newRoot;
+        }
+    }
+
+    deleteRotate(x, y, leaning, rotatingAroundRoot, rotateLeft, rotateRight) {
+        let newRoot = x;
+
+        let factor = balanceFactor(y);
+        switch (factor) {
+            case 0:
+            case leaning:
+                newRoot = rotateLeft(x);
+                break;
+            default:
+                rotateRight(y);
+                newRoot = rotateLeft(x);
+                break;
+        }
+
+        [newRoot.left, newRoot.right, newRoot].filter(x => x).forEach(n => {
+            updateRank(n)
+        });
+
+        if (rotatingAroundRoot) {
+            this.root = newRoot;
+        }
+        return factor == 0;
+    }
+
+    deleteFixup(y, parent) {
+        let x = (y) ? y : parent;
+
+        let factor = balanceFactor(x);
+        switch (factor) {
+            case 0:
+                updateRank(x);
+                return false;
+            case -1:
+            case 1:
+                return true;
+        }
+
+        let rotatingAroundRoot = x.parent == null;
+        let [z, leaning, toLeft, toRight] = [x.left, -1, rotateRight, rotateLeft];
+        if (factor == 2) {
+            [z, leaning, toLeft, toRight] = [x.right, 1, rotateLeft, rotateRight];
+        }
+
+        return this.deleteRotate(x, z, leaning, rotatingAroundRoot, toLeft, toRight);
+    }
+
+    deleteRebalance(node, parent) {
+        while (node || parent) {
+            this.deleteFixup(node, parent);
+            [node, parent] = [parent, (parent) ? parent.parent : null];
+        }
+    }
+}
\ No newline at end of file
diff --git a/node.js b/node.js
new file mode 100644
index 0000000..66135f2
--- /dev/null
+++ b/node.js
@@ -0,0 +1,172 @@
+const LEAF = 0;
+const UNARY = 1;
+const BINARY = 2;
+
+function nodeHeight(node) {
+    if (node == null) {
+        return -1;
+    }
+    return 1 + Math.max(nodeHeight(node.left), nodeHeight(node.right));
+}
+
+function nodeRank(node) {
+    if (node == null) {
+        return -1;
+    }
+    return node.rank;
+}
+
+function nodeDifference(node, parent) {
+    if (parent === undefined) {
+        parent = node != null ? node.parent : null;
+    }
+    return nodeRank(parent) - nodeRank(node);
+}
+
+function nodeDifferences(node) {
+    let r = nodeRank(node);
+    let left = null;
+    let right = null;
+
+    if (node != null) {
+        left = node.left;
+        right = node.right;
+    }
+
+    return [r - nodeRank(left), r - nodeRank(right)];
+}
+
+function rotateRight(x) {
+    let parent = x.parent;
+    let y = x.left;
+    // let z = x.right;
+
+    if (parent != null) {
+        if (parent.left === x) {
+            parent.left = y;
+        } else {
+            parent.right = y;
+        }
+    }
+
+    x.left = y.right;
+    if (x.left != null) {
+        x.left.parent = x;
+    }
+
+    y.right = x;
+    x.parent = y;
+    y.parent = parent;
+
+    return y;
+}
+
+function rotateLeft(x) {
+    let parent = x.parent;
+    // let y = x.left;
+    let z = x.right;
+
+    if (parent != null) {
+        if (parent.left === x) {
+            parent.left = z;
+        } else {
+            parent.right = z;
+        }
+    }
+
+    x.right = z.left;
+    if (x.right != null) {
+        x.right.parent = x;
+    }
+
+    z.left = x;
+    x.parent = z;
+    z.parent = parent;
+
+    return z;
+}
+
+function findParentNode(value, node, missing) {
+    if (missing === undefined) {
+        missing = true;
+    }
+
+    newNode = node
+
+    while (newNode && (missing || newNode.value != value)) {
+        node = newNode;
+        if (value < node.value) {
+            newNode = node.left;
+        } else if (node.value < value) {
+            newNode = node.right;
+        } else {
+            // same value
+            return null;
+        }
+    }
+
+    return node;
+}
+
+function nodeSearch(value, node) {
+    while (node && node.value != value) {
+        node = (value < node.value) ? node.left : node.right;
+    }
+
+    return node;
+}
+
+function nodeMinimum(node) {
+    while (node.left != null) {
+        node = node.left;
+    }
+    return node;
+}
+
+function nodeMaximum(node) {
+    while (node.right != null) {
+        node = node.right;
+    }
+    return node;
+}
+
+class Node {
+    constructor(value, left, right, parent) {
+        this.value = value;
+        this.rank = 0;
+
+        this.parent = parent || null;
+        this.left = left || null;
+        this.right = right || null;
+    }
+
+    type() {
+        if (this.left != null && this.right != null) {
+            return BINARY;
+        }
+
+        if (this.left != null || this.right != null) {
+            return UNARY;
+        }
+
+        return LEAF;
+    }
+
+    serialize() {
+        return `Node(value=${this.value}, rank = ${this.rank}, left=${this.left}, right=${this.right}, parent=${this.parent})`;
+    }
+
+    toString() {
+        return `Node(value=${this.value}, rank=${this.rank})`;
+    }
+
+    promote() {
+        this.rank++;
+        return this;
+    }
+
+    demote() {
+        this.rank--;
+        return this;
+    }
+}
\ No newline at end of file
diff --git a/ranked_tree.js b/ranked_tree.js
new file mode 100644
index 0000000..8bbcf8d
--- /dev/null
+++ b/ranked_tree.js
@@ -0,0 +1,165 @@
+class Queue {
+    constructor() {
+        this.q = [];
+    }
+
+    enqueue(x) {
+        this.q.push(x);
+    }
+
+    dequeue() {
+        return this.q.shift();
+    }
+
+    isEmpty() {
+        return this.q.length == 0;
+    }
+}
+
+class RankedTree {
+    constructor() {
+        this.root = null;
+    }
+
+    _getUnwrappedGraph() {
+        let result = "";
+
+        let q = new Queue();
+        q.enqueue(this.root);
+
+        let edges = [];
+        while (!q.isEmpty()) {
+            let node = q.dequeue();
+            if (!q) {
+                continue;
+            }
+
+            result += `"${node.toString()}" [label="${node.value}, ${node.rank}"];\n`;
+
+            [node.left, node.right].filter(child => child).forEach(child => {
+                edges.push([node, child]);
+                q.enqueue(child);
+            });
+        }
+
+        edges.forEach(vertices => {
+            let [u, v] = vertices;
+            result += `"${u.toString()}" -> "${v.toString()}" [label="${nodeDifference(v)}"]\n`;
+        });
+
+        return result;
+    }
+
+    toString() {
+        return `digraph {\n${this._getUnwrappedGraph()}}\n`;
+    }
+
+    rank() {
+        return nodeRank(this.root);
+    }
+
+    isCorrect() {
+        return this.isCorrectNode(this.root);
+    }
+
+    search(value, node) {
+        return nodeSearch(value, node || this.root);
+    }
+
+    insert(value) {
+        let insertedNode = new Node(value);
+
+        if (!this.root) {
+            this.root = insertedNode;
+            return;
+        }
+
+        let parent = findParentNode(value, this.root);
+        if (!parent) {
+            return;
+        }
+
+        insertedNode.parent = parent;
+
+        if (value < parent.value) {
+            parent.left = insertedNode;
+        } else {
+            parent.right = insertedNode;
+        }
+
+        this.insertRebalance(insertedNode);
+    }
+
+    transplant(u, v) {
+        if (!u.parent) {
+            this.root = v;
+        } else if (u.parent.left === u) {
+            u.parent.left = v;
+        } else {
+            u.parent.right = v;
+        }
+
+        if (v) {
+            v.rank = u.rank;
+            v.parent = u.parent;
+        }
+    }
+
+    deleteNode(node) {
+        if (!node) {
+            return null;
+        }
+
+        let [y, parent] = [null, node.parent];
+
+        if (!node.left) {
+            y = node.right;
+            this.transplant(node, node.right);
+        } else if (!node.right) {
+            y = node.left;
+            this.transplant(node, node.left);
+        } else {
+            let successor = nodeMinimum(node.right);
+            parent = (successor.parent != node) ? successor.parent : successor;
+
+            if (successor.parent != node) {
+                parent = (successor.right) ? successor.right : successor.parent;
+                this.transplant(successor, successor.right);
+                successor.right = node.right;
+                successor.right.parent = successor;
+            }
+
+            this.transplant(node, successor);
+            successor.left = node.left;
+            node.left.parent = successor;
+        }
+
+        return [y, parent];
+    }
+
+    delete(value) {
+        let node = this.root;
+        while (node && node.value != value) {
+            node = (value < node.value) ? node.left : node.right;
+        }
+
+        let toRebalance = this.deleteNode(node);
+        if (toRebalance) {
+            let [y, parent] = toRebalance;
+            this.deleteRebalance(y, parent);
+        }
+    }
+
+    /* abstract methods */
+    isCorrectNode(node) {
+        throw "not implemented!";
+    }
+
+    insertRebalance(node) {
+        throw "not implemented!";
+    }
+
+    deleteRebalance(node, parent) {
+        throw "not implemented!";
+    }
+}
\ No newline at end of file
diff --git a/ravl.js b/ravl.js
new file mode 100644
index 0000000..97bfcde
--- /dev/null
+++ b/ravl.js
@@ -0,0 +1,18 @@
+class RAVLTree extends WAVLTree {
+    isCorrectNode(node, recursive) {
+        if (!node) {
+            return true;
+        }
+
+        if (!nodeDifferences(node).filter(d => d <= 0).length > 0) {
+            return false;
+        }
+
+        return !recursive || (this.isCorrectNode(node.left) && this.isCorrectNode(node.right));
+    }
+
+    deleteRebalance(node, parent) {
+        // no-op
+        return;
+    }
+}
\ No newline at end of file
diff --git a/wavl.js b/wavl.js
new file mode 100644
index 0000000..71753bc
--- /dev/null
+++ b/wavl.js
@@ -0,0 +1,123 @@
+class WAVLTree extends AVLTree {
+    isCorrectNode(node, recursive) {
+        if (!node) {
+            return true;
+        }
+
+        nodeDifferences(node).forEach(childRank => {
+            if ([1, 2].findIndex(childRank) == -1) {
+                return false;
+            }
+        });
+
+        if (node.type() == LEAF) {
+            return node.rank == 0;
+        }
+
+        return !(recursive ?? true) || (this.isCorrectNode(node.left) && this.isCorrectNode(node.right));
+    }
+
+    fixDelete(x, y, z, reversed, rotateLeft, rotateRight) {
+        let newRoot = x;
+        let [v, w] = [y.left, y.right];
+
+        if (reversed) {
+            [v, w] = [w, v];
+        }
+
+        let wDiff = nodeDifference(w, y);
+
+        if (wDiff == 1 && y.parent) {
+            newRoot = rotateLeft(y.parent);
+
+            y.promote();
+            z.demote();
+
+            if (z.type() == LEAF) {
+                z.demote();
+            }
+        } else if (wDiff == 2 && v && v.parent) {
+            rotateRight(v.parent);
+            newRoot = rotateLeft(v.parent);
+
+            v.promote().promote();
+            y.demote();
+            z.demote().demote();
+        }
+
+        return newRoot;
+    }
+
+    bottomUpDelete(x, parent) {
+        let xDiff = nodeDifference(x, parent);
+        if (xDiff != 3 || !parent) {
+            return;
+        }
+
+        let y = (parent.left === x) ? parent.right : parent.left;
+        let yDiff = nodeDifference(y, parent);
+
+        while (parent && xDiff == 3 && y && (yDiff == 2 || nodeDifferences(y).equals([2, 2]))) {
+            parent.demote();
+            if (yDiff != 2) {
+                y.demote();
+            }
+
+            x = parent;
+            parent = x.parent;
+            if (!parent) {
+                return;
+            }
+
+            let y = (parent.left === x) ? parent.right : parent.left;
+
+            xDiff = nodeDifference(x, parent);
+            yDiff = nodeDifference(y, parent);
+        }
+
+        if (!parent) {
+            return;
+        }
+
+        let rotatingAroundRoot = parent.parent == null;
+        let newRoot = parent;
+
+        let parentNodeDiffs = nodeDifferences(parent);
+        if (parentNodeDiffs.sort().equals([1, 3])) {
+            if (parent.left === x) {
+                newRoot = this.fixDelete(x, parent.right, parent, false, rotateLeft, rotateRight);
+            } else {
+                newRoot = this.fixDelete(x, parent.left, parent, true, rotateRight, rotateLeft);
+            }
+        }
+
+        if (rotatingAroundRoot) {
+            this.root = newRoot;
+        }
+    }
+
+    deleteFixup(y, parent) {
+        let z = (y) ? y : parent;
+
+        if (nodeDifferences(z).equals([2, 2])) {
+            z.demote();
+        }
+
+        if (!parent) {
+            return;
+        }
+
+        [parent.left, parent.right].forEach(y => {
+            if (nodeDifference(y, parent) == 3) {
+                this.bottomUpDelete(y, parent);
+            }
+        });
+    }
+
+    deleteRebalance(node, parent) {
+        while (node || parent) {
+            this.deleteFixup(node, parent);
+            [node, parent] = parent, (parent) ? parent.parent : null;
+        }
+    }
+}
\ No newline at end of file