diff -r 0b7337826593 -r 3fd79fcdb491 src/Pure/Concurrent/single_assignment_sequential.ML
--- a/src/Pure/Concurrent/single_assignment_sequential.ML	Thu Feb 18 17:07:10 2016 +0100
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,30 +0,0 @@
-(*  Title:      Pure/Concurrent/single_assignment_sequential.ML
-    Author:     Makarius
-
-Single-assignment variables (sequential version).
-*)
-
-structure Single_Assignment: SINGLE_ASSIGNMENT =
-struct
-
-abstype 'a var = Var of 'a SingleAssignment.saref
-with
-
-fun var _ = Var (SingleAssignment.saref ());
-
-fun peek (Var var) = SingleAssignment.savalue var;
-
-fun await v =
-  (case peek v of
-    SOME x => x
-  | NONE => Thread.unavailable ());
-
-fun assign (v as Var var) x =
-  (case peek v of
-    SOME _ => raise Fail "Duplicate assignment to variable"
-  | NONE => SingleAssignment.saset (var, x));
-
-end;
-
-end;
-