diff --git a/index.js b/index.js
index 6b5736f..cb564b9 100644
--- a/index.js
+++ b/index.js
@@ -1,7 +1,13 @@
 function add(a ,b){
     return a + b
 }
+function sub(a, b){
+    if(!(a>b)) throw new Error (" no . a must be greater than b")
+    return a-b
+}
 
 add(2, 5)
 add(10, 25)
-add(2, 3)
\ No newline at end of file
+add(2, 3)
+
+sub(10 , 6)