diff --git a/src/main/java/me/hatter/math/Phi.java b/src/main/java/me/hatter/math/Phi.java
index 66dcbf1..f08a131 100644
--- a/src/main/java/me/hatter/math/Phi.java
+++ b/src/main/java/me/hatter/math/Phi.java
@@ -17,7 +17,9 @@ public class Phi {
     public static BigInteger phi(BigInteger n) {
         BigInteger p = BigInteger.valueOf(0);
         BigInteger i = BigInteger.valueOf(1);
+        // for i \in [1, n)
         while (i.compareTo(n) < 0) {
+            // gcd(i, n) = 1
             if (i.gcd(n).equals(BigInteger.ONE)) {
                 p = p.add(BigInteger.ONE);
             }