diff --git a/src/Assignment3/IntSet.sc b/src/Assignment3/IntSet.sc
new file mode 100644
index 0000000..a469e0b
--- /dev/null
+++ b/src/Assignment3/IntSet.sc
@@ -0,0 +1,27 @@
+abstract class IntSet() {
+  def add(x: Int): IntSet
+  def contains(x: Int): Boolean
+}
+
+class NonEmpty(elem: Int, left: IntSet, right: IntSet) extends IntSet() {
+  def add(x: Int): IntSet = {
+    if (x < elem) new NonEmpty(elem, left add x, right)
+    else if (x > elem) new NonEmpty(elem, left, right add x)
+    else this
+  }
+
+  def contains(x: Int): Boolean =
+    if (x < elem) left contains x
+    else if (x > elem) right contains x
+    else true
+}
+
+class Empty extends IntSet() {
+  def add(x: Int): IntSet = new NonEmpty(x, new Empty(), new Empty)
+  def contains(x: Int): Boolean = false
+}
+
+val t1 = new Empty()
+val t2 = t1 add 3
+val t3 = t1 add 4 add 5 add 2 add 6
+t3 contains 4
\ No newline at end of file
diff --git a/src/Lesson3/Rational2.sc b/src/Lesson3/Rational2.sc
index 3774328..d9fcc8f 100644
--- a/src/Lesson3/Rational2.sc
+++ b/src/Lesson3/Rational2.sc
@@ -1,31 +1,41 @@
-class Rational(n: Int, d: Int) {
-  def num = n
-  def denom = d
+import scala.annotation.tailrec
 
-  def add(that: Rational): Rational = new Rational(
+class Rational(n: Int, d: Int) {
+  require(d != 0)
+
+  @tailrec
+  private def gcd(x: Int, y: Int): Int =
+    if (y == 0) x else gcd(y, x % y)
+
+  private val g: Int = gcd(n, d)
+  def num: Int = n / g
+  def denom: Int = d / g
+
+
+  def +(that: Rational): Rational = new Rational(
     this.num * that.denom + this.denom * that.num,
     this.denom * that.denom
   )
 
-  def neg: Rational = new Rational(-num, denom)
+  def unary_- : Rational = new Rational(-num, denom)
 
-  def smallerThan(that: Rational): Boolean = this.num * that.denom < that.num * this.denom
+  def <(that: Rational): Boolean = this.num * that.denom < that.num * this.denom
 
-  def max(that: Rational): Rational = if (this.smallerThan(that)) that else this
+  def max(that: Rational): Rational = if (this < that) that else this
 
-  override def toString = num + "/" + denom
+  override def toString = if (math.abs(denom) == 1) "" + denom else num + "/" + denom
 }
 
 val r1 = new Rational(1, 3)
 val r2 = new Rational(2, 3)
-val r3 = r1.add(r2)
+val r3 = r1 + r2
 
 r3
 
-r2.neg
+-r2
 
-r2.smallerThan(r1)
-r2.smallerThan(r3)
+r2 < r1
+r2 < r3
 
 r2.max(r1)
 r2.max(r3)
\ No newline at end of file