diff --git a/sledge/semantics/llairScript.sml b/sledge/semantics/llairScript.sml
index db943571a..978491860 100644
--- a/sledge/semantics/llairScript.sml
+++ b/sledge/semantics/llairScript.sml
@@ -57,8 +57,10 @@ Datatype:
   | Select exp exp
   (* Args: Record, index, value *)
   | Update exp exp exp
-  (* Args: unsigned?, to-type, from-type, value *)
-  | Convert bool typ typ exp
+  (* Args: number of bits, integer expression, result type *)
+  | Signed num exp typ
+  (* Args: number of bits, integer expression, result type *)
+  | Unsigned num exp typ
 End
 
 Datatype:
@@ -215,17 +217,18 @@ Definition nfits_def:
     0 < size ∧ n < 2 ** size
 End
 
+Definition signed2unsigned_def:
+  signed2unsigned i size =
+    if i < 0 then Num (2 ** size + i) else Num i
+End
+
 (* Convert an integer to an unsigned number, following the 2's complement
  * representation, assuming (ifits i size). This is what OCaml's Z.extract does,
  * which is used in LLAIR for Convert expressions and unsigned operations, e.g.,
- * <. The difference between LLAIR's extract and i2n is that i2n assumes that i
- * fits into size rather than truncating it first. *)
+ * <. *)
 Definition i2n_def:
   i2n (IntV i size) : num =
-    if i < 0 then
-      Num (2 ** size + i)
-    else
-      Num i
+    signed2unsigned i size
 End
 
 (* Convert an unsigned number into the integer that it would be in 2's
@@ -320,17 +323,18 @@ Inductive eval_exp:
    ⇒
    eval_exp s (Update e1 e2 e3) (AggV (list_update r idx vals))) ∧
 
-  (∀s to_t from_t e v size.
-   eval_exp s e (FlatV v) ∧
-   size = sizeof_bits to_t
+  (∀s e i size to_t size1.
+   eval_exp s e (FlatV (IntV i size1)) ∧
+   size < sizeof_bits to_t
    ⇒
-   eval_exp s (Convert T to_t from_t e) (FlatV (IntV (truncate_2comp (&i2n v) size) size))) ∧
+   eval_exp s (Unsigned size e to_t)
+     (FlatV (IntV (&(signed2unsigned (truncate_2comp i size) size)) (sizeof_bits to_t)))) ∧
 
-  (∀s to_t from_t e size size1 i.
+  (∀s e size size1 i to_t.
    eval_exp s e (FlatV (IntV i size1)) ∧
-   size = sizeof_bits to_t
+   size ≤ sizeof_bits to_t
    ⇒
-   eval_exp s (Convert F to_t from_t e) (FlatV (IntV (truncate_2comp i size) size)))
+   eval_exp s (Signed size e to_t) (FlatV (IntV (truncate_2comp i size) (sizeof_bits to_t))))
 
 End
 
diff --git a/sledge/semantics/llair_propScript.sml b/sledge/semantics/llair_propScript.sml
index 4c3b1a44d..202771cb2 100644
--- a/sledge/semantics/llair_propScript.sml
+++ b/sledge/semantics/llair_propScript.sml
@@ -16,10 +16,28 @@ new_theory "llair_prop";
 
 numLib.prefer_num ();
 
+Theorem signed2unsigned_fits:
+  0 < n ∧ ifits i n ⇒ ifits (&signed2unsigned i n) (n + 1)
+Proof
+  rw [signed2unsigned_def, ifits_def]
+  >- (
+    `?j. i = -&j` by intLib.COOPER_TAC >>
+    rw [] >> fs [] >>
+    rfs [EXP_SUB] >>
+    `j ≤ 2 ** n` by intLib.COOPER_TAC >>
+    rw [INT_SUB, GSYM int_sub])
+  >- (
+    `?j. i = &j` by intLib.COOPER_TAC >>
+    rw [] >> fs [] >>
+    rw [INT_SUB, GSYM int_sub] >>
+    rfs [EXP_SUB] >>
+    intLib.COOPER_TAC)
+QED
+
 Theorem i2n_n2i:
-  !n size. 0 < size ⇒ (nfits n size ⇔ (i2n (n2i n size) = n))
+  ∀n size. 0 < size ⇒ (nfits n size ⇔ (i2n (n2i n size) = n))
 Proof
-  rw [nfits_def, n2i_def, i2n_def] >> rw []
+  rw [nfits_def, n2i_def, i2n_def, signed2unsigned_def] >> rw []
   >- intLib.COOPER_TAC
   >- (
     `2 ** size ≤ n` by intLib.COOPER_TAC >> simp [INT_SUB] >>
@@ -32,9 +50,9 @@ Proof
 QED
 
 Theorem n2i_i2n:
-  !i size. 0 < size ⇒ (ifits i size ⇔ (n2i (i2n (IntV i size)) size) = IntV i size)
+  ∀i size. 0 < size ⇒ (ifits i size ⇔ (n2i (i2n (IntV i size)) size) = IntV i size)
 Proof
-  rw [ifits_def, n2i_def, i2n_def] >> rw [] >> fs []
+  rw [ifits_def, n2i_def, i2n_def, signed2unsigned_def] >> rw [] >> fs []
   >- (
     eq_tac >> rw []
     >- (
@@ -44,7 +62,7 @@ Proof
     >- (
       fs [intLib.COOPER_PROVE ``∀(x:int) y z. x - y = z ⇔ x = y + z``] >>
       fs [INT_OF_NUM] >>
-      `?j. i = -j` by intLib.COOPER_TAC >> rw [] >> fs [] >>
+      `∃j. i = -j` by intLib.COOPER_TAC >> rw [] >> fs [] >>
       qpat_x_assum `_ ≤ Num _` mp_tac >>
       fs [GSYM INT_OF_NUM] >>
       ASM_REWRITE_TAC [GSYM INT_LE] >> rw [] >>
@@ -69,10 +87,10 @@ Proof
   >- intLib.COOPER_TAC
 QED
 
-Theorem w2n_i2n:
-  ∀w. w2n (w : 'a word) = i2n (IntV (w2i w) (dimindex (:'a)))
+Theorem w2n_signed2unsigned:
+  ∀w. w2n (w : 'a word) = signed2unsigned (w2i w) (dimindex (:'a))
 Proof
-  rw [i2n_def] >> Cases_on `w` >> fs []
+  rw [signed2unsigned_def] >> Cases_on `w` >> fs []
   >- (
     `INT_MIN (:α) ≤ n`
     by (
@@ -89,6 +107,12 @@ Proof
     rw [w2i_n2w_pos])
 QED
 
+Theorem w2n_i2n:
+  ∀w. w2n (w : 'a word) = i2n (IntV (w2i w) (dimindex (:'a)))
+Proof
+  rw [i2n_def] >> metis_tac [w2n_signed2unsigned]
+QED
+
 Theorem w2i_n2w:
   ∀n. n < dimword (:'a) ⇒ IntV (w2i (n2w n : 'a word)) (dimindex (:'a)) = n2i n (dimindex (:'a))
 Proof
@@ -130,7 +154,8 @@ Definition exp_uses_def:
   (exp_uses (Record es) = bigunion (set (map exp_uses es))) ∧
   (exp_uses (Select e1 e2) = exp_uses e1 ∪ exp_uses e2) ∧
   (exp_uses (Update e1 e2 e3) = exp_uses e1 ∪ exp_uses e2 ∪ exp_uses e3) ∧
-  (exp_uses (Convert _ _ _ e) = exp_uses e)
+  (exp_uses (Unsigned _ e _) = exp_uses e) ∧
+  (exp_uses (Signed _ e _) = exp_uses e)
 Termination
   WF_REL_TAC `measure exp_size` >> rw [] >>
   Induct_on `es` >> rw [exp_size_def] >> res_tac >> rw []
@@ -179,6 +204,122 @@ Proof
   metis_tac [eval_exp_ignores_unused_lem]
 QED
 
+Triviality num_mod_to_int_mod:
+  y ≠ 0 ⇒ x MOD y = Num (&x % &y)
+Proof
+  fs [INT_MOD]
+QED
+
+Triviality int_of_num2:
+  0 ≤ x ⇒ &Num x = x
+Proof
+  metis_tac [INT_OF_NUM]
+QED
+
+Theorem int_sub_mod:
+  ∀i j. j ≠ 0 ⇒ (i - j) % j = i % j
+Proof
+  rw [int_mod] >>
+  `-j % j = 0 ∧ -j / j = -1`
+  by (
+    ONCE_REWRITE_TAC [INT_NEG_MINUS1] >> rw [] >>
+    rw [INT_MUL_DIV]) >>
+  rw [INT_ADD_DIV, int_sub, INT_RDISTRIB] >>
+  rw [] >>
+  intLib.COOPER_TAC
+QED
+
+Theorem mod_halfway:
+  ∀i b. 0 < b ⇒ ((i + b) % (2 * b) - b < 0 ⇔ 0 ≤ i % (2 * b) - b)
+Proof
+  rw [] >> `b ≠ 0` by intLib.COOPER_TAC >>
+  rw [Once (GSYM INT_MOD_PLUS)] >>
+  `b < 2 * b` by intLib.COOPER_TAC >>
+  rw [INT_LESS_MOD] >>
+  `0 ≤ i % (2 * b) ∧ i % (2 * b) < 2 * b`
+  by (
+    `~(2 * b < 0) ∧ 2 * b ≠ 0` by intLib.COOPER_TAC >>
+    drule INT_MOD_BOUNDS >>
+    rw []) >>
+  `0 ≤ i % (2 * b) + b` by intLib.COOPER_TAC >>
+  Cases_on `i % (2 * b) + b < 2 * b` >> rw [INT_LESS_MOD]
+  >- intLib.COOPER_TAC >>
+  simp [Once (GSYM int_sub_mod)] >>
+  rw [intLib.COOPER_PROVE ``∀x (b:int). x + b - (2 * b) = x - b``] >>
+  `i % (2 * b) − b < 2 * b` by intLib.COOPER_TAC >>
+  `0 ≤ i % (2 * b) − b` by intLib.COOPER_TAC >>
+  rw [INT_LESS_MOD] >>
+  intLib.COOPER_TAC
+QED
+
+Theorem unsigned_truncate:
+  ∀m n i.
+    0 < m ∧ m ≤ n ∧ -i ≤ 2 ** n
+    ⇒
+    signed2unsigned (truncate_2comp i m) m = signed2unsigned i n MOD (2 ** m)
+Proof
+  rw [signed2unsigned_def, truncate_2comp_def] >>
+  qabbrev_tac `b = &(2 ** (m - 1))` >>
+  `&((2:num) ** m) = 2 * b`
+  by (rw [Abbr `b`] >> Cases_on `m` >> fs [ADD1, EXP_ADD]) >>
+  `0 < b` by rw [Abbr `b`] >>
+  `0 < 2 * b ∧ 0 ≠ 2 * b ∧ b < 2 * b` by (rw [Abbr `b`] >> intLib.COOPER_TAC) >>
+  asm_simp_tac std_ss [num_mod_to_int_mod] >>
+  fs [mod_halfway] >>
+  `∃x. &(2 ** n) = 2 * b * 2 ** x`
+  by (
+    rw [Abbr `b`, GSYM EXP_ADD] >>
+    `2 = 2 ** 1` by rw [] >>
+    `∀x. 2 * 2 ** (m + x - 1) = 2 ** (1 + (m + x - 1))` by metis_tac [EXP_ADD] >>
+    rw [] >>
+    qexists_tac `n - m` >> rw []) >>
+  irule (METIS_PROVE [] ``x = y ⇒ f x = f y``) >>
+  fs [GSYM int_le] >>
+  rw [int_of_num2] >>
+  rw [intLib.COOPER_PROVE ``∀(x:int) b. 2 * b + (x - b) = b + x``] >>
+  `0 ≤ i % (2 * b) ∧ i % (2 * b) < 2 * b`
+  by (
+    `~(2 * b < 0) ∧ 2 * b ≠ 0` by intLib.COOPER_TAC >>
+    drule INT_MOD_BOUNDS >>
+    rw [])
+  >- (
+    `0 ≤ 2 * b * &(2 ** x) + i` by intLib.COOPER_TAC >>
+    rw [int_of_num2] >>
+    `2 * b ≠ 0` by intLib.COOPER_TAC >>
+    drule INT_MOD_ADD_MULTIPLES >>
+    rw [Once INT_MUL_COMM] >>
+    rw [Once (GSYM INT_MOD_PLUS)] >>
+    rw [INT_LESS_MOD] >>
+    simp [Once (GSYM int_sub_mod)] >>
+    rw [intLib.COOPER_PROVE ``∀x (b:int). x + b - (2 * b) = x - b``] >>
+    `i % (2 * b) − b < 2 * b` by intLib.COOPER_TAC >>
+    rw [INT_LESS_MOD])
+  >- (
+    rw [Once (GSYM INT_MOD_PLUS)] >>
+    rw [INT_LESS_MOD] >>
+    simp [Once (GSYM int_sub_mod)] >>
+    rw [intLib.COOPER_PROVE ``∀x (b:int). x + b - (2 * b) = x - b``] >>
+    `i % (2 * b) − b < 2 * b` by intLib.COOPER_TAC >>
+    rw [INT_LESS_MOD])
+  >- (
+    `0 ≤ 2 * b * &(2 ** x) + i` by intLib.COOPER_TAC >>
+    rw [int_of_num2] >>
+    `2 * b ≠ 0` by intLib.COOPER_TAC >>
+    drule INT_MOD_ADD_MULTIPLES >>
+    rw [Once INT_MUL_COMM] >>
+    rw [Once (GSYM INT_MOD_PLUS)] >>
+    rw [INT_LESS_MOD] >>
+    `i % (2 * b) + b < 2 * b` by intLib.COOPER_TAC >>
+    rw [INT_LESS_MOD] >>
+    intLib.COOPER_TAC)
+  >- (
+    rw [Once (GSYM INT_MOD_PLUS)] >>
+    rw [INT_LESS_MOD] >>
+    `i % (2 * b) + b < 2 * b` by intLib.COOPER_TAC >>
+    rw [INT_LESS_MOD] >>
+    intLib.COOPER_TAC)
+QED
+
 (* Relate the semantics of Convert to something more closely following the
  * implementation *)
 
@@ -247,30 +388,6 @@ End
      Z.signed_extract i3 1 3 = Z.of_int (-3);;
      *)
 
-Definition extract_def:
-  extract (:'a) unsigned bits z =
-    if unsigned then Zextract (:'a) z 0 bits else Zsigned_extract (:'a) z 0 bits
-End
-
-Definition simp_convert_def:
-  simp_convert (:'a) unsigned dst src arg =
-    case (dst, src) of
-    | (IntegerT m, IntegerT n) =>
-      (if m ≤ n then
-        case arg of
-        | Integer data _ => Integer (extract (:'a) F m data) dst
-        | _ => Convert F dst src arg
-      else
-        case arg of
-        | Integer data _ => Integer (extract (:'a) unsigned n data) dst
-        | _ =>
-          if unsigned then Convert unsigned dst src arg
-          else arg)
-    | _ =>
-      if dst = src then arg
-      else Convert unsigned dst src arg
-End
-
 Theorem Zextract0:
   dimindex (:'b) ≤ dimindex (:'a)
   ⇒
@@ -306,93 +423,171 @@ Proof
   rw [w21_sw2sw_extend]
 QED
 
-Theorem convert_implementation_fits:
-  ∀unsigned dst src const i m n.
-    const = Integer i src ∧
-    src = IntegerT n ∧
-    dst = IntegerT m ∧ 0 < m ∧
-    ifits i (sizeof_bits src) ∧
-    dimindex (:'b) = min m n ∧
+Theorem signed_extract_truncate_2comp:
+  dimindex (:'b) ≤ dimindex (:'a)
+  ⇒
+  Zsigned_extract (:'a) i 0 (dimindex (:'b)) = truncate_2comp i (dimindex (:'b))
+Proof
+  rw [] >>
+  drule Zsigned_extract0 >> rw [] >>
+  metis_tac [truncate_2comp_i2w_w2i]
+QED
+
+Theorem unsigned_extract_truncate_2comp:
+  dimindex (:'b) ≤ dimindex (:'a)
+  ⇒
+  Zextract (:'a) i 0 (dimindex (:'b)) = &signed2unsigned (truncate_2comp i (dimindex (:'b))) (dimindex (:'b))
+Proof
+  rw [] >> drule Zextract0 >> rw [w2n_i2w] >>
+  `∃n. -i ≤ 2 ** n ∧ dimindex (:'b) ≤ n`
+  by (
+    Cases_on `i < 0` >> rw []
+    >- (
+      `∃j. i = -&j` by intLib.COOPER_TAC >>
+      rw [] >>
+      `1 < 2` by decide_tac >>
+      drule EXP_ALWAYS_BIG_ENOUGH >>
+      disch_then (qspec_then `j` mp_tac) >>
+      rw [] >>
+      qexists_tac `MAX m (dimindex (:'b))` >>
+      rw [MAX_DEF] >>
+      drule bitTheory.TWOEXP_MONO >>
+      intLib.COOPER_TAC)
+    >- (
+      `∃j. i = &j` by intLib.COOPER_TAC >>
+      rw [] >>
+      metis_tac [])) >>
+  `0 < dimword (:'b) ∧ 0 < dimindex (:'b)` by rw [DIMINDEX_GT_0, ZERO_LT_dimword] >>
+  `0 ≠ dimindex (:'b) ∧ 0 ≠ dimword (:'b)` by decide_tac >>
+  drule unsigned_truncate >>
+  ntac 2 (disch_then drule) >>
+  rw [GSYM dimword_def] >>
+  rw [signed2unsigned_def]
+  >- (
+    asm_simp_tac std_ss [GSYM INT_MOD] >>
+    `0 ≤ &(2 ** n) + i`
+    by (fs [INT_EXP] >> intLib.COOPER_TAC) >>
+    asm_simp_tac std_ss [int_of_num2] >>
+    `∃j. i = -&j` by intLib.COOPER_TAC >>
+    rw [] >>
+    `∃x. &(2 ** n) = dimword (:'b) * 2 ** x`
+    by (
+      rw [GSYM EXP_ADD, dimword_def] >>
+      qexists_tac `n - dimindex (:'b)` >> rw []) >>
+    rw [] >>
+    `&dimword (:β) ≠ 0` by intLib.COOPER_TAC >>
+    drule INT_MOD_ADD_MULTIPLES >>
+    simp_tac std_ss [Once INT_MUL_COMM, GSYM INT_MUL])
+  >- (
+    `∃j. i = &j` by intLib.COOPER_TAC >>
+    rw [])
+QED
+
+Definition simp_signed_def:
+  simp_signed (:'a) bits arg to_t =
+    case arg of
+    | Integer data _ => Integer (Zsigned_extract (:'a) data 0 bits) to_t
+    | _ => Signed bits arg to_t
+End
+
+Definition simp_unsigned_def:
+  simp_unsigned (:'a) bits arg to_t =
+    case arg of
+    | Integer data _ => Integer (Zextract (:'a) data 0 bits) to_t
+    | _ => Signed bits arg to_t
+End
+
+Theorem signed_implementation_fits:
+  ∀const i to_t from_t.
+    dimindex (:'b) ≤ sizeof_bits to_t ∧
     dimindex (:'b) ≤ dimindex (:'a)
     ⇒
-    ∃i2. simp_convert (:'a) unsigned dst src const = Integer i2 dst ∧ ifits i2 m
+    ∃i2.
+      simp_signed (:'a) (dimindex (:'b)) (Integer i from_t) to_t =
+      Integer i2 to_t ∧ ifits i2 (sizeof_bits to_t)
 Proof
-  rw [simp_convert_def, extract_def, MIN_DEF] >> fs []
-  >- (drule Zsigned_extract0 >> rw [] >> rw [ifits_w2i])
+  rw [simp_signed_def] >>
+  drule Zsigned_extract0 >> rw [] >>
+  `ifits (w2i (i2w i : 'b word)) (dimindex (:'b))` by metis_tac [ifits_w2i] >>
+  metis_tac [ifits_mono]
+QED
+
+Theorem unsigned_implementation_fits:
+  ∀const i to_t from_t.
+    dimindex (:'b) < sizeof_bits to_t ∧
+    dimindex (:'b) ≤ dimindex (:'a)
+    ⇒
+    ∃i2.
+      simp_unsigned (:'a) (dimindex (:'b)) (Integer i from_t) to_t =
+      Integer i2 to_t ∧ ifits i2 (sizeof_bits to_t)
+Proof
+  rw [simp_unsigned_def] >>
+  drule Zextract0 >> rw [] >> rw [w2n_i2w] >>
+  fs [ifits_def, dimword_def] >> rw [] >>
+  qspecl_then [`i`, `&(2 ** dimindex (:β))`] mp_tac INT_MOD_BOUNDS >>
+  rw []
   >- (
-    `m = dimindex (:'b)` by decide_tac >>
-     drule Zsigned_extract0 >> rw [] >> rw [ifits_w2i])
+    `0 <= (2:num) ** (sizeof_bits to_t − 1)` by intLib.COOPER_TAC >>
+    intLib.COOPER_TAC)
   >- (
-    drule Zextract0 >> rw [] >> rw [w2n_i2w] >> fs [sizeof_bits_def] >>
-    fs [ifits_def, dimword_def] >> rw [] >>
-    qspecl_then [`i`, `&(2 ** dimindex (:β))`] mp_tac INT_MOD_BOUNDS >>
-    rw []
-    >- intLib.COOPER_TAC >>
-    `dimindex (:'b) < m` by decide_tac >>
-    `2 ** dimindex (:'b) ≤ 2 ** (m - 1)` suffices_by intLib.COOPER_TAC >>
+    `2 ** dimindex (:'b) ≤ 2 ** (sizeof_bits to_t - 1)` suffices_by intLib.COOPER_TAC >>
     rw [])
-  >- (
-    drule Zsigned_extract0 >> rw [] >>
-    irule ifits_mono >> qexists_tac `dimindex (:'b)` >> rw [ifits_w2i])
 QED
 
-Theorem convert_implementation:
-  ∀h unsigned dst src const i m n.
-    const = Integer i src ∧
-    src = IntegerT n ∧ 0 < n ∧
-    dst = IntegerT m ∧
-    ifits i (sizeof_bits src) ∧
-    dimindex (:'b) = min m n ∧
-    dimindex (:'b) ≤ dimindex (:'a)
+Theorem signed_implementation:
+  ∀to_t i from_t h m n.
+    dimindex (:'b) ≤ sizeof_bits to_t ∧
+    dimindex (:'b) ≤ dimindex (:'a) ∧
+    from_t = IntegerT m ∧
+    to_t = IntegerT n ∧
+    0 < m ∧
+    ifits i m
     ⇒
-    eval_exp h (Convert unsigned dst src const) =
-    eval_exp h (simp_convert (:'a) unsigned dst src const)
+    eval_exp h (Signed (dimindex (:'b)) (Integer i from_t) to_t) =
+    eval_exp h (simp_signed (:'a) (dimindex (:'b)) (Integer i from_t) to_t)
 Proof
-  rw [EXTENSION, IN_DEF] >>
-  simp [simp_convert_def] >>
-  CASE_TAC >>
+  rw [EXTENSION, IN_DEF] >> simp [simp_signed_def] >>
   ONCE_REWRITE_TAC [eval_exp_cases] >>
-  fs [sizeof_bits_def] >>
+  fs [] >>
   ONCE_REWRITE_TAC [eval_exp_cases] >> rw [] >>
+  `0 < m` by decide_tac >>
+  `truncate_2comp i m = i` by metis_tac [fits_ident] >>
+  rw [] >> fs [sizeof_bits_def] >>
+  irule (METIS_PROVE [] ``y = z ⇒ (x = y ⇔ x = z)``) >> rw [] >>
+  rw [signed_extract_truncate_2comp] >>
+  `0 < dimindex (:'b)` by metis_tac [DIMINDEX_GT_0] >>
   `0 < n` by decide_tac >>
-  `truncate_2comp i n = i` by metis_tac [fits_ident] >>
-  rw [] >>
-  Cases_on `unsigned` >> fs [extract_def] >>
-  irule (METIS_PROVE [] ``y = z ⇒ (x = y ⇔ x = z)``) >> rw []
-  >- ( (* Truncating, unsigned convert *)
-    drule Zsigned_extract0 >> rw [] >>
-    `min m n = m` by fs [MIN_DEF] >>
-    `∀i. truncate_2comp i (dimindex (:β)) = w2i (i2w i : 'b word)`
-    by rw [GSYM truncate_2comp_i2w_w2i] >>
-    fs [] >> rw [i2w_pos, i2n_def, i2w_def] >>
-    `?j. 0 ≤ j ∧ -i = j` by rw [] >>
-    `i = -j` by intLib.COOPER_TAC >>
-    simp [] >>
-    simp [GSYM int_sub] >>
-    `?k. j = &k` by metis_tac [NUM_POSINT_EXISTS] >>
-    simp [] >>
-    `k < 2 ** n`
-    by (fs [ifits_def] >> Cases_on `n` >> fs [ADD1, EXP_ADD]) >>
-    simp [INT_SUB, word_2comp_n2w, dimword_def] >>
-    qabbrev_tac `d = dimindex (:'b)` >>
-    `∃x. (2:num) ** n = 2 ** x * 2 ** d`
-    by (
-      `?x. n = x + d` by (qexists_tac `n - d` >> fs [MIN_DEF]) >>
-      metis_tac [EXP_ADD]) >>
-    metis_tac [MOD_COMPLEMENT, bitTheory.ZERO_LT_TWOEXP, MULT_COMM])
-  >- ( (* Truncating, signed convert *)
-    `min m n = m` by rw [MIN_DEF] >>
-    drule Zsigned_extract0 >> rw [] >> fs [] >>
-    `w2i (i2w i : 'b word) = truncate_2comp i m` by metis_tac [truncate_2comp_i2w_w2i] >>
-    rw [] >>
-    `0 < dimindex (:'b)` by rw [] >>
-    metis_tac [fits_ident, truncate_2comp_fits]) >>
-  (* extending *)
-    drule Zsigned_extract0 >> drule Zextract0 >> fs [MIN_DEF] >> rw [w2n_i2n] >>
-    `INT_MIN (:'b) ≤ i ∧ i ≤ INT_MAX (:'b)` suffices_by metis_tac [w2i_i2w] >>
-    fs [ifits_def, INT_MAX_def, INT_MIN_def, int_arithTheory.INT_NUM_SUB] >>
-    rw [DECIDE ``!(x:num). x < 1 ⇔ x = 0``,
-        intLib.COOPER_PROVE``!(x:int). x ≤ y -1 ⇔ x < y``]
+  `ifits (truncate_2comp i (dimindex (:β))) n` suffices_by metis_tac [fits_ident] >>
+  metis_tac [truncate_2comp_fits, ifits_mono]
+QED
+
+Theorem unsigned_implementation:
+  ∀to_t i from_t h m n.
+    dimindex (:'b) < sizeof_bits to_t ∧
+    dimindex (:'b) ≤ dimindex (:'a) ∧
+    from_t = IntegerT m ∧
+    to_t = IntegerT n ∧
+    0 < m ∧
+    ifits i m
+    ⇒
+    eval_exp h (Unsigned (dimindex (:'b)) (Integer i from_t) to_t) =
+    eval_exp h (simp_unsigned (:'a) (dimindex (:'b)) (Integer i from_t) to_t)
+Proof
+  rw [EXTENSION, IN_DEF] >> simp [simp_unsigned_def] >>
+  ONCE_REWRITE_TAC [eval_exp_cases] >>
+  fs [] >>
+  ONCE_REWRITE_TAC [eval_exp_cases] >> rw [] >>
+  `0 < m` by decide_tac >>
+  `truncate_2comp i m = i` by metis_tac [fits_ident] >>
+  rw [] >> fs [sizeof_bits_def] >>
+  irule (METIS_PROVE [] ``y = z ⇒ (x = y ⇔ x = z)``) >> rw [] >>
+  rw [unsigned_extract_truncate_2comp] >>
+  `0 < dimindex (:'b)` by metis_tac [DIMINDEX_GT_0] >>
+  `0 < n` by decide_tac >>
+  `ifits (&signed2unsigned (truncate_2comp i (dimindex (:β))) (dimindex (:'b))) n` suffices_by metis_tac [fits_ident] >>
+  irule ifits_mono >>
+  qexists_tac `dimindex (:'b) + 1` >> rw [] >>
+  metis_tac [truncate_2comp_fits, signed2unsigned_fits]
 QED
 
 export_theory ();
diff --git a/sledge/semantics/llvm_to_llairScript.sml b/sledge/semantics/llvm_to_llairScript.sml
index 03b5430c3..d099415a9 100644
--- a/sledge/semantics/llvm_to_llairScript.sml
+++ b/sledge/semantics/llvm_to_llairScript.sml
@@ -131,7 +131,10 @@ Definition translate_instr_to_exp_def:
   (translate_instr_to_exp gmap emap (Insertvalue _ (t1, a1) (t2, a2) cs) =
     translate_updatevalue gmap (translate_arg gmap emap a1) (translate_arg gmap emap a2) cs) ∧
   (translate_instr_to_exp gmap emap (Cast _ cop (t1, a1) t) =
-    Convert (cop ≠ Sext) (translate_ty t) (translate_ty t1) (translate_arg gmap emap a1))
+    (if cop = Zext then Unsigned else Signed)
+      (sizeof_bits (translate_ty (if cop = Trunc then t else t1)))
+      (translate_arg gmap emap a1)
+      (translate_ty t))
 End
 
 (* This translation of insertvalue to update and select is quadratic in the
diff --git a/sledge/semantics/llvm_to_llair_propScript.sml b/sledge/semantics/llvm_to_llair_propScript.sml
index b92921a6f..b94a19c6f 100644
--- a/sledge/semantics/llvm_to_llair_propScript.sml
+++ b/sledge/semantics/llvm_to_llair_propScript.sml
@@ -825,47 +825,102 @@ Proof
   metis_tac [EVERY2_LUPDATE_same, LIST_REL_LENGTH, LIST_REL_EL_EQN]
 QED
 
+val sizes = [``:1``, ``:8``, ``:32``, ``:64``];
+
 val trunc_thms =
   LIST_CONJ (map (fn x => SIMP_RULE (srw_ss()) [] (INST_TYPE [``:'a`` |-> x] truncate_2comp_i2w_w2i))
-                 [``:1``, ``:8``, ``:32``, ``:64``]);
-
-val i2n_thms =
-  LIST_CONJ (map (fn x => SIMP_RULE (srw_ss()) [] (INST_TYPE [``:'a`` |-> x] (GSYM w2n_i2n)))
-                 [``:1``, ``:8``, ``:32``, ``:64``]);
+                 sizes);
+
+val signed2unsigned_thms =
+  LIST_CONJ (map (fn x => SIMP_RULE (srw_ss()) [] (INST_TYPE [``:'a`` |-> x] (GSYM w2n_signed2unsigned)))
+                 sizes);
+
+Definition good_cast_def:
+  (good_cast Trunc (FlatV (IntV i size)) from_bits to_t ⇔
+    from_bits = size ∧ llair$sizeof_bits to_t < from_bits) ∧
+  (good_cast Zext (FlatV (IntV i size)) from_bits to_t ⇔
+    from_bits = size ∧ from_bits < sizeof_bits to_t) ∧
+  (good_cast Sext (FlatV (IntV i size)) from_bits to_t ⇔
+    from_bits = size ∧ from_bits < sizeof_bits to_t) ∧
+  (good_cast Ptrtoint _ _ _ ⇔ T) ∧
+  (good_cast Inttoptr _ _ _ ⇔ T)
+End
 
 Theorem translate_cast_correct:
-  ∀prog gmap emap s1' cop ty v1 v1' e1' result t2.
-    do_cast cop v1.value ty = Some result ∧
+  ∀prog gmap emap s1' cop from_bits to_ty v1 v1' e1' result.
+    do_cast cop v1.value to_ty = Some result ∧
     eval_exp s1' e1' v1' ∧
     v_rel v1.value v1' ∧
-    (cop = Inttoptr ⇒ ∃t. ty = PtrT t)
+    good_cast cop v1' from_bits (translate_ty to_ty)
     ⇒
     ∃v3'.
-      eval_exp s1' (Convert (cop ≠ Sext) (translate_ty ty) t2 e1') v3' ∧
+      eval_exp s1' ((if (cop = Zext) then Unsigned else Signed)
+                    (if cop = Trunc then sizeof_bits (translate_ty to_ty) else from_bits)
+                    e1' (translate_ty to_ty)) v3' ∧
       v_rel result v3'
 Proof
-  rw [] >> simp [Once eval_exp_cases, PULL_EXISTS, Once v_rel_cases] >>
-  Cases_on `cop ≠ Sext`
-  >- (
-    Cases_on `cop` >> fs [do_cast_def] >> rw [] >>
-    BasicProvers.EVERY_CASE_TAC >> fs [] >>
-    fs [OPTION_JOIN_EQ_SOME, w64_cast_some, signed_v_to_int_some,
-        unsigned_v_to_num_some, mk_ptr_some] >>
+  rw [] >> simp [Once eval_exp_cases, PULL_EXISTS, Once v_rel_cases]
+  >- ( (* Zext *)
+    fs [do_cast_def, OPTION_JOIN_EQ_SOME, unsigned_v_to_num_some, w64_cast_some,
+       translate_ty_def, sizeof_bits_def, translate_size_def] >>
+    rw [] >>
+    rfs [v_rel_cases] >> rw [] >>
+    qmatch_assum_abbrev_tac `eval_exp _ _ (FlatV (IntV i s))` >>
+    qexists_tac `i` >> qexists_tac `s` >> rw [] >>
+    unabbrev_all_tac >>
+    fs [good_cast_def, translate_ty_def, sizeof_bits_def, translate_size_def] >>
+    rw [trunc_thms, signed2unsigned_thms] >>
+    rw [GSYM w2w_def, w2w_w2w, WORD_ALL_BITS] >>
+    rw [w2i_w2w_expand])
+  >- ( (* Trunc *)
+    fs [do_cast_def] >> rw [] >>
+    fs [OPTION_JOIN_EQ_SOME, w64_cast_some, unsigned_v_to_num_some,
+        signed_v_to_int_some, mk_ptr_some] >>
     rw [sizeof_bits_def, translate_ty_def, translate_size_def] >>
     rfs [] >> fs [v_rel_cases] >>
-    HINT_EXISTS_TAC >>
-    rw [w2w_n2w, trunc_thms, i2n_thms, w2w_def, pointer_size_def]) >>
-  fs [do_cast_def, OPTION_JOIN_EQ_SOME, PULL_EXISTS, w64_cast_some,
-      translate_ty_def, sizeof_bits_def, signed_v_to_int_some,
-      translate_size_def] >>
-  rfs [v_rel_cases, w2w_i2w] >> rw [trunc_thms] >>
-  qmatch_assum_abbrev_tac `eval_exp _ _ (FlatV (IntV i s))` >>
-  qexists_tac `s` >> qexists_tac `i` >> rw [] >>
-  unabbrev_all_tac >> rw [] >>
-  rw [i2w_w2i_extend, WORD_w2w_OVER_MUL, WORD_ALL_BITS] >>
-  Cases_on `w2w w : word1` >> rw [] >> fs [dimword_1] >>
-  Cases_on `n` >> rw [] >> fs [] >>
-  Cases_on `n'` >> rw [] >> fs []
+    rw [] >>
+    qmatch_assum_abbrev_tac `eval_exp _ _ (FlatV (IntV i s))` >>
+    qexists_tac `s` >> qexists_tac `i` >> rw [] >>
+    unabbrev_all_tac >>
+    fs [good_cast_def, translate_ty_def, sizeof_bits_def, translate_size_def] >>
+    rw [w2w_n2w, GSYM w2w_def, trunc_thms, pointer_size_def] >>
+    rw [i2w_w2i_extend, WORD_w2w_OVER_MUL] >>
+    rw [w2w_w2w, WORD_ALL_BITS, word_bits_w2w] >>
+    rw [word_mul_def]) >>
+  Cases_on `cop` >> fs [] >> rw []
+  >- ( (* Sext *)
+    fs [do_cast_def] >> rw [] >>
+    fs [OPTION_JOIN_EQ_SOME, w64_cast_some, unsigned_v_to_num_some,
+        signed_v_to_int_some, mk_ptr_some] >>
+    rw [sizeof_bits_def, translate_ty_def, translate_size_def] >>
+    rfs [] >> fs [v_rel_cases] >>
+    rw [] >>
+    qmatch_assum_abbrev_tac `eval_exp _ _ (FlatV (IntV i s))` >>
+    qexists_tac `s` >> qexists_tac `i` >> rw [] >>
+    unabbrev_all_tac >>
+    fs [good_cast_def, translate_ty_def, sizeof_bits_def, translate_size_def] >>
+    rw [trunc_thms, w2w_i2w] >>
+    irule (GSYM w2i_i2w)
+    >- (
+      `w2i w ≤ INT_MAX (:1) ∧ INT_MIN (:1) ≤ w2i w` by metis_tac [w2i_le, w2i_ge] >>
+      fs [] >> intLib.COOPER_TAC)
+    >- (
+      `w2i w ≤ INT_MAX (:1) ∧ INT_MIN (:1) ≤ w2i w` by metis_tac [w2i_le, w2i_ge] >>
+      fs [] >> intLib.COOPER_TAC)
+    >- (
+      `w2i w ≤ INT_MAX (:1) ∧ INT_MIN (:1) ≤ w2i w` by metis_tac [w2i_le, w2i_ge] >>
+      fs [] >> intLib.COOPER_TAC)
+    >- (
+      `w2i w ≤ INT_MAX (:8) ∧ INT_MIN (:8) ≤ w2i w` by metis_tac [w2i_le, w2i_ge] >>
+      fs [] >> intLib.COOPER_TAC)
+    >- (
+      `w2i w ≤ INT_MAX (:8) ∧ INT_MIN (:8) ≤ w2i w` by metis_tac [w2i_le, w2i_ge] >>
+      fs [] >> intLib.COOPER_TAC)
+    >- (
+      `w2i w ≤ INT_MAX (:32) ∧ INT_MIN (:32) ≤ w2i w` by metis_tac [w2i_le, w2i_ge] >>
+      fs [] >> intLib.COOPER_TAC))
+  (* TODO: pointer to int and int to pointer casts *)
+  >> cheat
 QED
 
 Theorem prog_ok_nonterm:
@@ -1056,7 +1111,8 @@ Proof
       rw [] >> metis_tac [] ))>>
   conj_tac
   >- ( (* Cast *)
-    rw [step_instr_cases, get_instr_cases, update_result_def] >>
+    simp [step_instr_cases, get_instr_cases, update_result_def] >>
+    rpt strip_tac >>
     qpat_x_assum `Cast _ _ _ _ = el _ _` (assume_tac o GSYM) >>
     `arg_to_regs a1 ⊆ live prog s1.ip`
     by (
@@ -1065,16 +1121,16 @@ Proof
       metis_tac []) >>
     fs [] >>
     first_x_assum (mp_then.mp_then mp_then.Any mp_tac translate_arg_correct) >>
-    disch_then drule >> disch_then drule >> rw [] >>
+    disch_then drule >> disch_then drule >> strip_tac >>
     drule translate_cast_correct >> ntac 2 (disch_then drule) >>
     simp [] >>
-    disch_then (qspec_then `translate_ty t1` mp_tac) >>
+    disch_then (qspec_then `sizeof_bits (translate_ty t1)` mp_tac) >>
     impl_tac
     (* TODO: prog_ok should enforce that the type is consistent *)
     >- cheat >>
-    rw [] >>
-    rename1 `eval_exp _ (Convert _ _ _ _) res_v` >>
-    rw [inc_pc_def, llvmTheory.inc_pc_def] >>
+    strip_tac >>
+    rename1 `eval_exp _ _ res_v` >>
+    simp [inc_pc_def, llvmTheory.inc_pc_def] >>
     rename1 `r ∈ _` >>
     `assigns prog s1.ip = {r}`
     by rw [assigns_cases, EXTENSION, IN_DEF, get_instr_cases, instr_assigns_def] >>
@@ -1085,15 +1141,17 @@ Proof
       simp [get_instr_cases, PULL_EXISTS] >>
       ntac 3 (disch_then drule) >>
       simp [terminator_def, next_ips_cases, IN_DEF, inc_pc_def]) >>
-    Cases_on `r ∈ regs_to_keep` >> rw []
+    Cases_on `r ∈ regs_to_keep` >> simp []
     >- (
       simp [step_inst_cases, PULL_EXISTS] >>
       qexists_tac `res_v` >> rw [] >>
+      fs [] >>
       rw [update_results_def, GSYM FUPDATE_EQ_FUPDATE_LIST] >>
       irule mem_state_rel_update_keep >> rw [])
     >- (
-      irule mem_state_rel_update >> rw []
+      irule mem_state_rel_update >> simp [] >> strip_tac
       >- (
+        rw [] >>
         fs [exp_uses_def] >> Cases_on `a1` >> fs [translate_arg_def] >>
         rename1 `flookup _ r_tmp` >>
         qexists_tac `r_tmp` >> rw [] >>
diff --git a/sledge/semantics/miscScript.sml b/sledge/semantics/miscScript.sml
index 35083da7f..f15ed6c80 100644
--- a/sledge/semantics/miscScript.sml
+++ b/sledge/semantics/miscScript.sml
@@ -570,6 +570,12 @@ Proof
   metis_tac [MOD_MULT_MOD, bitTheory.ZERO_LT_TWOEXP]
 QED
 
+Theorem w2i_w2w_expand:
+  dimindex (:'a) < dimindex (:'b) ⇒ w2i (w2w (w : 'a word) : 'b word) = &w2n w
+Proof
+  rw [w2i_def, w2n_w2w, word_msb, word_bit_thm, w2w]
+QED
+
 (* ----- Theorems about lazy lists ----- *)
 
 Theorem toList_some: