diff --git a/deque/src/deque/Main.java b/deque/src/deque/Main.java
index 1eaf481..be044bf 100644
--- a/deque/src/deque/Main.java
+++ b/deque/src/deque/Main.java
@@ -4,15 +4,141 @@ import tester.Tester;
 
 class Examples {
 
+    Deque<Integer> mtDeque;
+
+    Deque<String> exampleDeque;
     Sentinel<String> exampleSentinel;
 
+    Deque<Integer> oneTwo;
+    Node<Integer> one;
+    Node<Integer> two;
+
     void init() {
+        mtDeque = new Deque<Integer>();
+
         exampleSentinel = new Sentinel<String>();
+        exampleDeque = new Deque<String>(exampleSentinel);
+
+        Node<String> n1 = new Node<String>("abc");
+        Node<String> n2 = new Node<String>("bcd");
+        Node<String> n3 = new Node<String>("def");
+
+        exampleSentinel.assign(n3, n1);
+        n1.assign(exampleSentinel, n2);
+        n2.assign(n1, n3);
+        n3.assign(n2, exampleSentinel);
+
+        one = new Node<Integer>(1);
+        two = new Node<Integer>(2);
+
+        oneTwo = new Deque<Integer>();
+
+        oneTwo.header.assign(two, one);
+        one.assign(oneTwo.header, two);
+        two.assign(one, oneTwo.header);
     }
 
-    void testSentinel(Tester t) {
+    void testDequeSize(Tester t) {
         init();
-        t.checkExpect(exampleSentinel.nxt, exampleSentinel);
+        t.checkExpect(mtDeque.size(), 0);
+        t.checkExpect(exampleDeque.size(), 3);
+    }
+
+    void testDequeAddAtHead(Tester t) {
+        init();
+
+        t.checkExpect(mtDeque.addAtHead(2).addAtHead(1), oneTwo);
+    }
+
+    void testDequeAddAtTail(Tester t) {
+        init();
+
+        t.checkExpect(mtDeque.addAtTail(1).addAtTail(2), oneTwo);
+    }
+
+    void testDequeRemoveFromHead(Tester t) {
+        init();
+
+        Deque<Integer> justTwo = new Deque<Integer>().addAtHead(2);
+        t.checkExpect(oneTwo.removeFromHead(), justTwo);
+        t.checkException(
+            new UnsupportedOperationException(
+                "Can't remove a `Sentinel` node."
+            ),
+            mtDeque,
+            "removeFromHead"
+        );
+    }
+
+    void testDequeRemoveFromTail(Tester t) {
+        init();
+
+        Deque<Integer> justOne = new Deque<Integer>().addAtHead(1);
+        t.checkExpect(oneTwo.removeFromTail(), justOne);
+        t.checkException(
+            new UnsupportedOperationException(
+                "Can't remove a `Sentinel` node."
+            ),
+            mtDeque,
+            "removeFromTail"
+        );
+    }
+
+    void testDequeFind(Tester t) {
+        init();
+
+        t.checkExpect(oneTwo.find(new isTwo()), two);
+        t.checkExpect(
+            oneTwo.find(new isTwoThousandOneHundredFortyFive()),
+            oneTwo.header
+        );
+        t.checkExpect(mtDeque.find(new isTwo()), mtDeque.header);
+    }
+}
+
+class Deque<T> {
+
+    ANode<T> header;
+
+    Deque() {
+        this.header = new Sentinel<T>();
+    }
+
+    Deque(Sentinel<T> sentinel) {
+        this.header = sentinel;
+    }
+
+    // Get number of `Node`s in the list (not counting `Sentinel`s).
+    int size() {
+        return this.header.sz();
+    }
+
+    // Add an element to the 'head' of the list.
+    Deque<T> addAtHead(T thing) {
+        this.header.addAtHead(thing);
+        return this;
+    }
+
+    // Add an element to the 'head' of the list.
+    Deque<T> addAtTail(T thing) {
+        this.header.addAtTail(thing);
+        return this;
+    }
+
+    // Remove the first element in the list.
+    Deque<T> removeFromHead() {
+        this.header.removeFromHead();
+        return this;
+    }
+
+    // Remove the last element in the list.
+    Deque<T> removeFromTail() {
+        this.header.removeFromTail();
+        return this;
+    }
+
+    ANode<T> find(IPred<T> question) {
+        return this.header.find(question);
     }
 }
 
@@ -27,23 +153,75 @@ abstract class ANode<T> {
         this.pre = pre;
     }
 
-    void assignNode(ANode<T> nxt, ANode<T> pre) {
+    void setNxt(ANode<T> nxt) {
+        this.nxt = nxt;
+    }
+
+    void setPre(ANode<T> pre) {
+        this.pre = pre;
+    }
+
+    void assign(ANode<T> pre, ANode<T> nxt) {
+        this.setPre(pre);
+        this.setNxt(nxt);
+    }
+
+    // Get the size of a list, not including the `Sentinel`.
+    int sz() {
         throw new UnsupportedOperationException(
-            "Can't call assignNode() on non-Node."
+            "Can't call `sz()` on non-`Sentinel` node."
         );
     }
-}
 
-class Deque<A> {
+    int szHelper() {
+        return 1 + this.nxt.szHelper();
+    }
 
-    Sentinel<A> sentinel;
+    void addAtHead(T thing) {
+        throw new UnsupportedOperationException(
+            "Can't call `addAtHead()` on non-`Sentinel` node."
+        );
+    }
 
-    Deque(Sentinel<A> sentinel) {
-        this.sentinel = sentinel;
+    void addAtTail(T thing) {
+        throw new UnsupportedOperationException(
+            "Can't call `addAtTail()` on non-`Sentinel` node."
+        );
+    }
+
+    void removeFromHead() {
+        throw new UnsupportedOperationException(
+            "Can't call `removeHead()` on non-`Sentinel` node."
+        );
+    }
+
+    void removeFromTail() {
+        throw new UnsupportedOperationException(
+            "Can't call `removeTail()` on non-`Sentinel` node."
+        );
+    }
+
+    // Set surrounding nodes to pass over this one.
+    void remove() {
+        this.nxt.setPre(this.pre);
+        this.pre.setNxt(this.nxt);
+        this.nxt = null;
+        this.pre = null;
+    }
+
+    ANode<T> find(IPred<T> question) {
+        throw new UnsupportedOperationException(
+            "Can't call `find()` on non-`Sentinel` node."
+        );
+    }
+
+    ANode<T> findHelper(IPred<T> question) {
+        return this;
     }
 }
 
-class Sentinel<T> extends ANode<ANode<T>> {
+// The sentinel of the list, linking its head and tail.
+class Sentinel<T> extends ANode<T> {
 
     Sentinel() {
         // To create an empty list, this Sentinel points to itself.
@@ -51,9 +229,44 @@ class Sentinel<T> extends ANode<ANode<T>> {
         this.nxt = this;
         this.pre = this;
     }
+
+    int sz() {
+        return this.nxt.szHelper();
+    }
+
+    int szHelper() {
+        return 0;
+    }
+
+    void addAtHead(T thing) {
+        new Node<T>(thing, this, this.nxt);
+    }
+
+    void addAtTail(T thing) {
+        new Node<T>(thing, this.pre, this);
+    }
+
+    void removeFromHead() {
+        this.nxt.remove();
+    }
+
+    void removeFromTail() {
+        this.pre.remove();
+    }
+
+    void remove() {
+        throw new UnsupportedOperationException(
+            "Can't remove a `Sentinel` node."
+        );
+    }
+
+    ANode<T> find(IPred<T> question) {
+        return this.nxt.findHelper(question);
+    }
 }
 
-class Node<T> extends ANode<Node<T>> {
+// A node in the list.
+class Node<T> extends ANode<T> {
 
     T val;
 
@@ -62,14 +275,39 @@ class Node<T> extends ANode<Node<T>> {
         this.val = val;
     }
 
-    Node(T val, ANode<T> nxt, ANode<T> pre) {
+    Node(T val, ANode<T> pre, ANode<T> nxt) {
         this(val);
-        this.assignNode(nxt, pre);
+        if (nxt == null || pre == null) throw new IllegalArgumentException(
+            "Can't construct node with defunct fields."
+        );
+
+        this.nxt = nxt;
+        this.pre = pre;
+
+        nxt.setPre(this);
+        pre.setNxt(this);
     }
 
-    void assignNode(ANode<T> nxt, ANode<T> pre) {
-        throw new UnsupportedOperationException(
-            "Can't call assignNode() on non-Node."
-        );
+    ANode<T> findHelper(IPred<T> question) {
+        return question.ask(this.val) ? this : this.nxt.findHelper(question);
+    }
+}
+
+// A predicate.
+interface IPred<T> {
+    boolean ask(T thing);
+}
+
+class isTwo implements IPred<Integer> {
+
+    public boolean ask(Integer n) {
+        return n == 2;
+    }
+}
+
+class isTwoThousandOneHundredFortyFive implements IPred<Integer> {
+
+    public boolean ask(Integer n) {
+        return n == 2145;
     }
 }
diff --git a/mastermind/.classpath b/mastermind/.classpath
index 3d02881..91fefed 100644
--- a/mastermind/.classpath
+++ b/mastermind/.classpath
@@ -6,7 +6,7 @@
 		</attributes>
 	</classpathentry>
 	<classpathentry kind="src" path="src"/>
-    <classpathentry kind="lib" path="/home/jacob/School/CS3/libs/javalib.jar"/>
-    <classpathentry kind="lib" path="/home/jacob/School/CS3/libs/tester.jar"/>
+    <classpathentry kind="lib" path="/home/jacob/Projects/CS3/libs/javalib.jar"/>
+    <classpathentry kind="lib" path="/home/jacob/Projects/CS3/libs/tester.jar"/>
 	<classpathentry kind="output" path="bin"/>
 </classpath>