diff --git a/scheme/ikarus.compiler.altcogen.ss b/scheme/ikarus.compiler.altcogen.ss
index dbf6cc3..f086840 100644
--- a/scheme/ikarus.compiler.altcogen.ss
+++ b/scheme/ikarus.compiler.altcogen.ss
@@ -245,7 +245,7 @@
 
 (define (insert-stack-overflow-check x)
   (define who 'insert-stack-overflow-check)
-   (define (NonTail x)
+  (define (NonTail x)
     (struct-case x
       [(constant)                 #f]
       [(var)                      #f]
@@ -275,32 +275,78 @@
       [(jmpcall label rator arg*) (or (NonTail rator) (ormap NonTail arg*))]
       [(mvcall rator k) #t] ; punt
       [else (error who "invalid expr" x)]))
- 
   (define (insert-check x)
     (make-seq (make-primcall '$stack-overflow-check '()) x))
-
   (define (ClambdaCase x)
     (struct-case x
       [(clambda-case info body)
        (make-clambda-case info (Main body))]))
-  ;;;
   (define (Clambda x)
     (struct-case x
       [(clambda label case* cp free* name)
        (make-clambda label (map ClambdaCase case*) cp free* name)]))
-  ;;;
   (define (Main x)
     (if (Tail x) 
         (insert-check x) 
         x))
-  ;;;
   (define (Program x)
     (struct-case x 
       [(codes code* body)
        (make-codes (map Clambda code*) (Main body))]))
-  ;;;
   (Program x))
 
+
+
+(define (insert-dummy-type-annotations x)
+  (define who 'insert-dummy-type-annotations)
+  (define (Closure x)
+    (struct-case x
+      [(closure code free*) 
+       x]
+       ;(make-closure (Expr code) (map Var free*))]
+      [else (error who "not a closure" x)]))
+  (define (Expr x)
+    (struct-case x
+      [(constant i) 
+       (make-known x 'constant i)]
+      [(var)      x]
+      [(primref op) 
+       (make-known x 'primitive op)]
+      [(bind lhs* rhs* body)
+       (make-bind lhs* (map Expr rhs*) (Expr body))]
+      [(fix lhs* rhs* body)
+       (make-fix lhs* (map Closure rhs*) (Expr body))]
+      [(conditional e0 e1 e2)
+       (make-conditional (Expr e0) (Expr e1) (Expr e2))]
+      [(seq e0 e1)
+       (make-seq (Expr e0) (Expr e1))]
+      [(primcall op arg*)         
+       (make-primcall op (map Expr arg*))]
+      [(forcall op arg*)
+       (make-forcall op (map Expr arg*))]
+      [(funcall rator arg*)
+       (make-funcall (Expr rator) (map Expr arg*))]
+      [(jmpcall label rator arg*) 
+       (make-jmpcall label (Expr rator) (map Expr arg*))]
+      [(mvcall rator k)
+       (make-mvcall (Expr rator) (Expr k))]
+      [else (error who "invalid expr" x)]))
+  (define (ClambdaCase x)
+    (struct-case x
+      [(clambda-case info body)
+       (make-clambda-case info (Expr body))]))
+  (define (Clambda x)
+    (struct-case x
+      [(clambda label case* cp free* name)
+       (make-clambda label (map ClambdaCase case*) cp free* name)]))
+  (define (Program x)
+    (struct-case x 
+      [(codes code* body)
+       (make-codes (map Clambda code*) (Expr body))]))
+  (Program x))
+
+
+
 (include "pass-specify-rep.ss")
 
 (define parameter-registers '(%edi)) 
@@ -2921,6 +2967,7 @@
          [x (eliminate-fix x)]
          [x (insert-engine-checks x)]
          [x (insert-stack-overflow-check x)]
+         ;[x (insert-dummy-type-annotations x)]
          [x (specify-representation x)]
          [x (impose-calling-convention/evaluation-order x)]
          [x (time-it "frame" (lambda () (assign-frame-sizes x)))]
diff --git a/scheme/ikarus.compiler.ss b/scheme/ikarus.compiler.ss
index ae0d046..f09931a 100644
--- a/scheme/ikarus.compiler.ss
+++ b/scheme/ikarus.compiler.ss
@@ -137,7 +137,7 @@
 (define-struct assign (lhs rhs))
 (define-struct mvcall (producer consumer))
 
-
+(define-struct known (expr type value))
 
 (define-struct shortcut (body handler))
 
diff --git a/scheme/last-revision b/scheme/last-revision
index 0d4b7f5..994cddf 100644
--- a/scheme/last-revision
+++ b/scheme/last-revision
@@ -1 +1 @@
-1476
+1478
diff --git a/scheme/pass-specify-rep.ss b/scheme/pass-specify-rep.ss
index b82414a..1599b86 100644
--- a/scheme/pass-specify-rep.ss
+++ b/scheme/pass-specify-rep.ss
@@ -139,11 +139,14 @@
         [else
          (let-values ([(lhs* rhs* arg*) (S* (cdr ls))])
            (let ([a (car ls)])
-             (cond
-               [(constant? a) 
+             (struct-case a
+               [(known expr type v)
+                (let ([tmp (unique-var 'tmp)])
+                  (values (cons tmp lhs*)
+                          (cons (V expr) rhs*)
+                          (cons (make-known tmp type v) arg*)))]
+               [(constant i)
                 (values lhs* rhs* (cons a arg*))]
-               ;[(var? a)
-               ; (values lhs* rhs* (cons a arg*))]
                [else
                 (let ([t (unique-var 'tmp)])
                   (values (cons t lhs*) (cons (V a) rhs*) (cons t arg*)))])))]))
@@ -348,7 +351,13 @@
         [(object? c) (error 'constant-rep "double-wrap")]
         [else (make-constant (make-object c))])))
 
-  (define (V x)
+  (define (V x) ;;; erase known values
+    (struct-case x 
+      [(known x type value)
+       (unknown-V x)]
+      [else (unknown-V x)]))
+
+  (define (unknown-V x)
     (struct-case x
       [(constant) (constant-rep x)]
       [(var)      x]
@@ -396,6 +405,9 @@
       [(funcall) (prm '!= (V x) (V (K #f)))]
       [(jmpcall) (prm '!= (V x) (V (K #f)))]
       [(forcall) (prm '!= (V x) (V (K #f)))]
+      [(known expr type val)
+       ;;; FIXME: suboptimal
+       (P expr)]
       [else (error 'cogen-P "invalid pred expr" x)])) 
   
   (define (E x)
@@ -421,6 +433,9 @@
        (make-funcall (Function rator) (map V arg*))]
       [(jmpcall label rator arg*)
        (make-jmpcall label (V rator) (map V arg*))]
+      [(known expr type val)
+       ;;; FIXME: suboptimal
+       (E expr)]
       [else (error 'cogen-E "invalid effect expr" x)]))
 
   (define (Function x)
@@ -476,6 +491,7 @@
     (struct-case x
       [(var) x]
       [(constant i) (constant-rep x)]
+      [(known expr type val) (T expr)]
       [else (error 'cogen-T "invalid" (unparse x))]))
 
   (define (ClambdaCase x)