diff --git a/main.janet b/main.janet
index 1d7aabd..057143c 100644
--- a/main.janet
+++ b/main.janet
@@ -10,5 +10,23 @@
                         ['* a (diff b var)]])
         (errorf "unknown op: %v" op)))))
 
-(pp (diff '(+ (* x x) 3) 'x))
-(pp (diff '(+ x 3) 'x))
+(defn simplify [expr]
+  (cond
+    (symbol? expr) expr
+    (number? expr) expr
+    (match expr [op & args]
+      (do
+        (def args (map simplify args))
+        (case op
+          '+ (do
+               (def terms (filter |(not= $ 0) args))
+               (if (= (length terms) 1) (first terms) ['+ ;terms]))
+          '* (cond
+               (find |(= $ 0) args) 0
+               (find |(= $ 1) args) (first (filter |(not= $ 1) args))
+               ['* ;args]) # otherwise leave unchanged
+          [op ;args])))))
+
+
+(pp (simplify (diff '(+ (* x x) 3) 'x)))
+(pp (simplify (diff '(+ x 3) 'x)))