diff --git a/basis/Weak.580.sml b/basis/Weak.580.sml
deleted file mode 100644
index aee1c736..00000000
--- a/basis/Weak.580.sml
+++ /dev/null
@@ -1,61 +0,0 @@
-(*
-    Title:      Weak references
-    Author:     David Matthews
-    Copyright   David Matthews 2008, 2015-16
-
-    This library is free software; you can redistribute it and/or
-    modify it under the terms of the GNU Lesser General Public
-    License version 2.1 as published by the Free Software Foundation.
-    
-    This library is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-    Lesser General Public License for more details.
-    
-    You should have received a copy of the GNU Lesser General Public
-    License along with this library; if not, write to the Free Software
-    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
-*)
-
-(* A weak reference or array contains option values.  The SOME variant of
-   the option must contain a reference.  This restriction is imposed because
-   they require pointer equality.  A weak reference or array behaves just like
-   a normal ref or array with one difference.  The garbage collector may set
-   a weak ref or the field of weak array to NONE if it currently contains
-   SOME r but r is not reachable other than through weak references.  The
-   one proviso is that if r is contained in the executable it is always
-   reachable.
-*)
-
-signature WEAK =
-sig
-    val weak: 'a ref option -> 'a ref option ref
-    val weakArray: int * 'a ref option -> 'a ref option array
-    val weakLock: Thread.Mutex.mutex
-    and weakSignal: Thread.ConditionVar.conditionVar
-    val touch : 'a ref -> unit
-end;
-
-structure Weak: WEAK =
-struct
-    fun weak (v: 'a ref option): 'a ref option ref = RunCall.allocateWordMemory(0w1, 0wx60, v)
-    
-    fun weakArray(n: int, v: 'a ref option): 'a ref option array =
-    let
-        val () = if n < 0 orelse n >= Array.maxLen then raise Size else ()
-        val arr = RunCall.allocateWordMemory(Word.fromInt n, 0wx60, v)
-    in
-        arr
-    end
-
-    val weakLock = Thread.Mutex.mutex()
-    and weakSignal = Thread.ConditionVar.conditionVar()
-
-    (* touch is considered by the compiler as an access to the ref but doesn't
-       actually do anything with it.  The idea is that it ensures that when a ref
-       is used as a token that this will access the ref and avoid the weak
-       reference becoming set to NONE.  It's primarily there for long-term
-       security in the event that the compiler is sufficiently clever to
-       work out that something is no longer referenced. *)
-    fun touch v = v := !v
-end;