diff --git a/piclib/built-in.scm b/piclib/built-in.scm
index 98988950..53ba52ed 100644
--- a/piclib/built-in.scm
+++ b/piclib/built-in.scm
@@ -140,6 +140,11 @@
 	     (any pred (cdr list))))
        (pred (car list)))))
 
+(define (fold f s xs)
+  (if (null? xs)
+      s
+      (fold f (f (car xs) s) (cdr xs))))
+
 (define (map f list . lists)
   (define (single-map f list)
     (if (null? list)
@@ -404,6 +409,14 @@
       (vector-copy! res 0 v start end)
       res)))
 
+(define (vector-append . vs)
+  (define (vector-append-2-inv w v)
+    (let ((res (make-vector (+ (vector-length v) (vector-length w)))))
+      (vector-copy! res 0 v)
+      (vector-copy! res (vector-length v) w)
+      res))
+  (fold vector-append-2-inv #() vs))
+
 ;;; 6.9 bytevector
 
 (define (bytevector . objs)