diff --git a/asllib/ASTUtils.ml b/asllib/ASTUtils.ml
index dfa6dc9c4..efc7df1f7 100644
--- a/asllib/ASTUtils.ml
+++ b/asllib/ASTUtils.ml
@@ -323,6 +323,7 @@ let rec expr_equal eq e1 e2 =
       o1 = o2 && expr_equal eq e11 e12 && expr_equal eq e21 e22
   | E_Binop _, _ | _, E_Binop _ -> false
   | E_Call (x1, args1, _), E_Call (x2, args2, _) ->
+      (* We can ignore parameters as they are deduced from arguments. *)
       String.equal x1 x2 && list_equal (expr_equal eq) args1 args2
   | E_Call _, _ | _, E_Call _ -> false
   | E_Concat li1, E_Concat li2 -> list_equal (expr_equal eq) li1 li2
@@ -423,7 +424,17 @@ and bitfield_equal eq bf1 bf2 =
       String.equal name1 name2
       && slices_equal eq slices1 slices2
       && bitfields_equal eq bf1' bf2'
-  | _ -> false
+  | BitField_Type (name1, slices1, t1), BitField_Type (name2, slices2, t2) ->
+      String.equal name1 name2
+      && slices_equal eq slices1 slices2
+      && type_equal eq t1 t2
+  | BitField_Simple _, BitField_Nested _
+  | BitField_Simple _, BitField_Type _
+  | BitField_Nested _, BitField_Simple _
+  | BitField_Nested _, BitField_Type _
+  | BitField_Type _, BitField_Nested _
+  | BitField_Type _, BitField_Simple _ ->
+      false
 
 let var_ x = E_Var x |> add_dummy_pos
 let binop op = map2_desc (fun e1 e2 -> E_Binop (op, e1, e2))
diff --git a/asllib/StaticInterpreter.ml b/asllib/StaticInterpreter.ml
index 3daf0a469..bcd3c3c3b 100644
--- a/asllib/StaticInterpreter.ml
+++ b/asllib/StaticInterpreter.ml
@@ -208,7 +208,7 @@ and slices_to_positions env =
 
 module Normalize = struct
   type atom = identifier
-  type 'a disjunction = Disjunction of 'a list
+  (** Our basic variables. *)
 
   module AtomOrdered = struct
     type t = atom
@@ -217,7 +217,15 @@ module Normalize = struct
   end
 
   module AMap = Map.Make (AtomOrdered)
+  (** A map from atoms. *)
+
+  (** A unitary monomial.
+
+      They are unitary in the sense that they do not have any factors:
+      {m 3 \times X^2 } is not unitary, while {m x^2 } is.
 
+      For example: {m X^2 + Y^4 } represented by {m X \to 2, Y \to 4 },
+      and {m 1 } is represented by the empty map. *)
   type monomial =
     | Prod of int AMap.t  (** Maps each variable to its exponent. *)
 
@@ -227,6 +235,7 @@ module Normalize = struct
     let compare (Prod ms1) (Prod ms2) = AMap.compare Int.compare ms1 ms2
   end
 
+  (** A map from a monomial. *)
   module MMap = struct
     include Map.Make (MonomialOrdered)
 
@@ -237,9 +246,23 @@ module Normalize = struct
         m empty
   end
 
+  (** A polynomial.
+
+      For example, {m X^2 - X + 4 } is represented by
+      {m X^2 \to 1, X \to -1, 1 \to 4 } *)
   type polynomial =
     | Sum of Z.t MMap.t  (** Maps each monomial to its factor. *)
 
+  module PolynomialOrdered = struct
+    type t = polynomial
+
+    let compare (Sum p1) (Sum p2) = MMap.compare Z.compare p1 p2
+  end
+
+  module PMap = Map.Make (PolynomialOrdered)
+  (** Map from polynomials. *)
+
+  (** A constraint on a numerical value. *)
   type sign =
     | Null
     | StrictPositive
@@ -248,16 +271,20 @@ module Normalize = struct
     | StrictNegative
     | NotNull
 
-  module PolynomialOrdered = struct
-    type t = polynomial
+  (** A conjunctive logical formulae with polynomials.
 
-    let compare (Sum p1) (Sum p2) = MMap.compare Z.compare p1 p2
-  end
+      For example, {m X^2 \leq 0 } is represented with {m X^2 \to \leq 0 }.
+  *)
+  type ctnts = Conjunction of sign PMap.t | Bottom
 
-  module PMap = Map.Make (PolynomialOrdered)
+  (** Case disjunctions. *)
+  type 'a disjunction = Disjunction of 'a list
 
-  type ctnts = Conjunction of sign PMap.t | Bottom
   type ir_expr = (ctnts * polynomial) disjunction
+  (** Constrained polynomials.
+
+      This is a branched tree of polynomials.
+  *)
   (* Wanted invariants for (e : ir_expr) :
      ⋁ {c | (c, d) ∈ e } <=> true                           (I₂)
      ∀ (cᵢ, eᵢ), (cⱼ, eⱼ) ∈ e, i != j => cⱼ ∩ cⱼ = ∅        (I₃)
@@ -542,8 +569,9 @@ module Normalize = struct
     | E_Binop (MUL, e1, e2) ->
         let ir1 = to_ir env e1 and ir2 = to_ir env e2 in
         cross_num ir1 ir2 mult_polys
-    | E_Binop (SHL, e1, { desc = E_Literal (L_Int i2); _ }) ->
-        let ir1 = to_ir env e1 and f2 = Z.pow Z.one (Z.to_int i2) in
+    | E_Binop (SHL, e1, { desc = E_Literal (L_Int i2); _ }) when Z.leq Z.zero i2
+      ->
+        let ir1 = to_ir env e1 and f2 = Z.shift_left Z.one (Z.to_int i2) in
         map_num
           (fun (Sum monos) -> Sum (MMap.map (fun c -> Z.mul c f2) monos))
           ir1