diff --git a/src/lisp.c b/src/lisp.c
index 56f626e..a314a09 100644
--- a/src/lisp.c
+++ b/src/lisp.c
@@ -2711,7 +2711,7 @@ static inline LispVal *copy_number(LispVal *v) {
     } else if (INTEGERP(v)) {
         return make_lisp_integer(((LispInteger *) v)->value);
     } else {
-        abort();
+        Fthrow(Qtype_error, Qnil);
     }
 }
 
@@ -2719,10 +2719,10 @@ DEFUN(add, "+", (LispVal * args)) {
     if (NILP(args)) {
         return make_lisp_integer(0);
     }
-    LispVal *out = copy_number(Fhead(args));
-    FOREACH(arg, Ftail(args)) {
+    LispVal *out = copy_number(HEAD(args));
+    FOREACH(arg, TAIL(args)) {
         LispVal *old_out = out;
-        WITH_CLEANUP_DOUBLE_PTR(old_out, {
+        WITH_CLEANUP(old_out, {
             ONE_MATH_OPERAION(+, out, out, arg); //
         });
     }
@@ -2733,16 +2733,64 @@ DEFUN(sub, "-", (LispVal * args)) {
     if (NILP(args)) {
         return make_lisp_integer(0);
     }
-    LispVal *out = copy_number(Fhead(args));
-    FOREACH(arg, Ftail(args)) {
+    LispVal *out = copy_number(HEAD(args));
+    FOREACH(arg, TAIL(args)) {
         LispVal *old_out = out;
-        WITH_CLEANUP_DOUBLE_PTR(old_out, {
+        WITH_CLEANUP(old_out, {
             ONE_MATH_OPERAION(-, out, out, arg); //
         });
     }
     return out;
 }
 
+DEFUN(mul, "*", (LispVal * args)) {
+    if (NILP(args)) {
+        return make_lisp_integer(1);
+    }
+    LispVal *out = copy_number(HEAD(args));
+    FOREACH(arg, TAIL(args)) {
+        LispVal *old_out = out;
+        WITH_CLEANUP(old_out, {
+            ONE_MATH_OPERAION(*, out, out, arg); //
+        });
+    }
+    return out;
+}
+
+DEFUN(div, "/", (LispVal * first, LispVal *rest)) {
+    if (NILP(rest)) {
+        if (INTEGERP(first)) {
+            return make_lisp_float(1.0 / ((LispInteger *) first)->value);
+        } else if (FLOATP(first)) {
+            return make_lisp_float(1.0 / ((LispFloat *) first)->value);
+        } else {
+            Fthrow(Qtype_error, Qnil);
+        }
+    }
+    LispVal *out = copy_number(HEAD(rest));
+    FOREACH(arg, TAIL(rest)) {
+        LispVal *old_out = out;
+        WITH_CLEANUP(old_out, {
+            ONE_MATH_OPERAION(*, out, out, arg); //
+        });
+    }
+    if (FLOATP(first)) {
+        LispVal *old_out = out;
+        ONE_MATH_OPERAION(/, out, first, out);
+        refcount_unref(old_out);
+    } else if (INTEGERP(first)) {
+        LispVal *old_out = out;
+        LispVal *ff = make_lisp_float(((LispInteger *) first)->value);
+        ONE_MATH_OPERAION(/, out, ff, out);
+        refcount_unref(ff);
+        refcount_unref(old_out);
+    } else {
+        refcount_unref(out);
+        Fthrow(Qtype_error, Qnil);
+    }
+    return out;
+}
+
 // ####################
 // # Vector Functions #
 // ####################
@@ -3434,6 +3482,8 @@ static void register_symbols_and_functions(void) {
     REGISTER_FUNCTION(add, "(&rest nums)", "Return the sun of NUMS.");
     REGISTER_FUNCTION(sub, "(&rest nums)",
                       "Return (head NUMS) - (apply '+ (tail NUMS)).");
+    REGISTER_FUNCTION(mul, "(&rest nums)", "");
+    REGISTER_FUNCTION(div, "(first &rest rest)", "");
     REGISTER_FUNCTION(
         if, "(cond then &rest else)",
         "Evaluate THEN if COND is non-nil, otherwise evaluate ELSE.");
diff --git a/src/lisp.h b/src/lisp.h
index 66c2cdf..bcbbe56 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -540,6 +540,8 @@ DECLARE_FUNCTION(num_eq, (LispVal * n1, LispVal *n2));
 DECLARE_FUNCTION(num_gt, (LispVal * n1, LispVal *n2));
 DECLARE_FUNCTION(add, (LispVal * args));
 DECLARE_FUNCTION(sub, (LispVal * args));
+DECLARE_FUNCTION(mul, (LispVal * args));
+DECLARE_FUNCTION(div, (LispVal * first, LispVal *rest));
 
 // ####################
 // # Vector Functions #