diff --git a/lib.py b/lib.py
index f7fbfa2..0f03c5d 100644
--- a/lib.py
+++ b/lib.py
@@ -83,8 +83,6 @@ def execute(program):
                 return reduce(lambda a, b: (a[0], a[1]*b[1]), subs[1:])
             elif ctx[0] == _ident("/"):
                 return reduce(lambda a, b: (a[0], a[1]/b[1]), subs[1:])
-            elif ctx[0] == _ident("%"):
-                return (subs[1][0], subs[1][1]%subs[2][1])
             elif ctx[0] == _ident("=="):
                 return ("number", 1.0 if subs[1] == subs[2] else 0.0)
             elif ctx[0] == _ident("="):
diff --git a/lib/aids.klambda b/lib/aids.klambda
index 2df0a3b..699875c 100644
--- a/lib/aids.klambda
+++ b/lib/aids.klambda
@@ -5,4 +5,5 @@ INCLUDE:./loop.klambda
 INCLUDE:./lists.klambda
 INCLUDE:./kokoro.klambda
 INCLUDE:./booleans.klambda
-INCLUDE:./string.klambda
\ No newline at end of file
+INCLUDE:./string.klambda
+INCLUDE:./math.klambda
\ No newline at end of file
diff --git a/lib/math.klambda b/lib/math.klambda
new file mode 100644
index 0000000..92102bd
--- /dev/null
+++ b/lib/math.klambda
@@ -0,0 +1,9 @@
+(def % (lambda (a m)
+    (cond (== m a)
+        0
+        (cond (< m a)
+            (% (- a m) m)
+            (- a 0)
+        )
+    )
+))
\ No newline at end of file