diff --git a/polynomial.js b/polynomial.js
index 0410cd9..ad2a899 100644
--- a/polynomial.js
+++ b/polynomial.js
@@ -30,6 +30,50 @@ function add(p1, p2) {
 }
 exports.add = add;
 
+function sub(p1, p2) {
+    let n;
+    if (p1.mod !== p2.mod) {
+        throw "different modulo"
+    } else {
+        n = p1.mod;
+    }
+    let len_p1 = p1.coefficients.length;
+    let len_p2 = p2.coefficients.length;
+    result = new Array(Math.max(len_p1, len_p2)).fill(0);
+    if (len_p1 > len_p2) {
+        for (let x = 0; x < len_p1 - len_p2; x++) p2.coefficients.push(0);
+    } else {
+        for (let x = 0; x < len_p2 - len_p1; x++) p1.coefficients.push(0);
+    }
+    for (let i = 0; i < result.length; i++) {
+        result[i] = (p1.coefficients[i] - p2.coefficients[i]) % n;
+    }
+    return new Polynomial(n, result);
+}
+exports.sub = sub;
+
+function sub(p1, p2) {
+    let n;
+    if (p1.mod !== p2.mod) {
+        throw "different modulo"
+    } else {
+        n = p1.mod;
+    }
+    let len_p1 = p1.coefficients.length;
+    let len_p2 = p2.coefficients.length;
+    result = new Array(Math.max(len_p1, len_p2)).fill(0);
+    if (len_p1 > len_p2) {
+        for (let x = 0; x < len_p1 - len_p2; x++) p2.coefficients.push(0);
+    } else {
+        for (let x = 0; x < len_p2 - len_p1; x++) p1.coefficients.push(0);
+    }
+    for (let i = 0; i < result.length; i++) {
+        result[i] = (p1.coefficients[i] - p2.coefficients[i]) % n;
+    }
+    return new Polynomial(n, result);
+}
+exports.add = add;
+
 function multiply(p1, p2) {
     let n;
     if (p1.mod !== p2.mod) {