diff --git a/Arm/BitVec.lean b/Arm/BitVec.lean
index 82dc029e..24dad21f 100644
--- a/Arm/BitVec.lean
+++ b/Arm/BitVec.lean
@@ -43,12 +43,13 @@ attribute [bitvec_rules] BitVec.msb_zero
 attribute [bitvec_rules] BitVec.toNat_cast
 attribute [bitvec_rules] BitVec.getLsbD_cast
 attribute [bitvec_rules] BitVec.getMsbD_cast
-attribute [bitvec_rules] BitVec.toNat_ofInt
+-- attribute [bitvec_rules] BitVec.toNat_ofInt -- TODO: not tagged bv_toNat.
+attribute [bv_toNat] BitVec.toNat_ofInt
 attribute [bitvec_rules] BitVec.toInt_ofInt
 attribute [bitvec_rules] BitVec.ofInt_natCast
 attribute [bitvec_rules] BitVec.toNat_zeroExtend'
-attribute [bitvec_rules] BitVec.toNat_zeroExtend
-attribute [bitvec_rules] BitVec.toNat_truncate
+-- attribute [bitvec_rules] BitVec.toNat_zeroExtend
+-- attribute [bitvec_rules] BitVec.toNat_truncate
 attribute [bitvec_rules] BitVec.zeroExtend_zero
 attribute [bitvec_rules] BitVec.ofNat_toNat
 attribute [bitvec_rules] BitVec.getLsbD_zeroExtend'
@@ -82,7 +83,7 @@ attribute [bitvec_rules] BitVec.toNat_xor
 attribute [bitvec_rules] BitVec.toFin_xor
 attribute [bitvec_rules] BitVec.getLsbD_xor
 attribute [bitvec_rules] BitVec.truncate_xor
-attribute [bitvec_rules] BitVec.toNat_not
+-- attribute [bitvec_rules] BitVec.toNat_not
 attribute [bitvec_rules] BitVec.toFin_not
 attribute [bitvec_rules] BitVec.getLsbD_not
 attribute [bitvec_rules] BitVec.truncate_not
@@ -90,7 +91,7 @@ attribute [bitvec_rules] BitVec.not_cast
 attribute [bitvec_rules] BitVec.and_cast
 attribute [bitvec_rules] BitVec.or_cast
 attribute [bitvec_rules] BitVec.xor_cast
-attribute [bitvec_rules] BitVec.toNat_shiftLeft
+-- attribute [bitvec_rules] BitVec.toNat_shiftLeft
 attribute [bitvec_rules] BitVec.toFin_shiftLeft
 attribute [bitvec_rules] BitVec.getLsbD_shiftLeft
 attribute [bitvec_rules] BitVec.getMsbD_shiftLeft
@@ -124,23 +125,24 @@ attribute [bitvec_rules] BitVec.not_concat
 attribute [bitvec_rules] BitVec.concat_or_concat
 attribute [bitvec_rules] BitVec.concat_and_concat
 attribute [bitvec_rules] BitVec.concat_xor_concat
-attribute [bitvec_rules] BitVec.toNat_add
+-- attribute [bitvec_rules] BitVec.toNat_add
 attribute [bitvec_rules] BitVec.toFin_add
 attribute [bitvec_rules] BitVec.ofFin_add
 attribute [bitvec_rules] BitVec.add_ofFin
 attribute [bitvec_rules] BitVec.add_zero
 attribute [bitvec_rules] BitVec.zero_add
 attribute [bitvec_rules] BitVec.toInt_add
-attribute [bitvec_rules] BitVec.toNat_sub
+-- attribute [bitvec_rules] BitVec.toNat_sub
+attribute [bv_toNat] toNat_sub
 attribute [bitvec_rules] BitVec.toFin_sub
 attribute [bitvec_rules] BitVec.ofFin_sub
 attribute [bitvec_rules] BitVec.sub_ofFin
 attribute [bitvec_rules] BitVec.sub_zero
 attribute [bitvec_rules] BitVec.sub_self
-attribute [bitvec_rules] BitVec.toNat_neg
+-- attribute [bitvec_rules] BitVec.toNat_neg
 attribute [bitvec_rules] BitVec.toFin_neg
 attribute [bitvec_rules] BitVec.neg_zero
-attribute [bitvec_rules] BitVec.toNat_mul
+-- attribute [bitvec_rules] BitVec.toNat_mul
 attribute [bitvec_rules] BitVec.toFin_mul
 attribute [bitvec_rules] BitVec.mul_zero
 attribute [bitvec_rules] BitVec.mul_one
@@ -246,6 +248,10 @@ attribute [bitvec_rules] Nat.reduceLeDiff
 attribute [bitvec_rules] Nat.reduceSubDiff
 attribute [bitvec_rules] BitVec.toNat_ofNat
 
+-- This might be a neccesary evil: it introduces a modulus,
+-- but it's also really useful.
+attribute [bitvec_rules] BitVec.toNat_ofNat
+
 -- Some Fin lemmas useful for bitvector reasoning:
 attribute [bitvec_rules] Fin.eta
 attribute [bitvec_rules] Fin.isLt
diff --git a/Arm/Memory/SeparateAutomation.lean b/Arm/Memory/SeparateAutomation.lean
index 88b3c8da..29ac674c 100644
--- a/Arm/Memory/SeparateAutomation.lean
+++ b/Arm/Memory/SeparateAutomation.lean
@@ -405,7 +405,7 @@ def simpAndIntroDef (name : String) (hdefVal : Expr) : SimpMemM FVarId  := do
 
     /- Simp to gain some more juice out of the defn.. -/
     let mut simpTheorems : Array SimpTheorems := #[]
-    for a in #[`minimal_theory, `bitvec_rules] do
+    for a in #[`minimal_theory, `bitvec_rules, `bv_toNat] do
       let some ext ← (getSimpExtension? a)
         | throwError m!"[simp_mem] Internal error: simp attribute {a} not found!"
       simpTheorems := simpTheorems.push (← ext.getTheorems)
diff --git a/Proofs/Popcount32.lean b/Proofs/Popcount32.lean
index a00aa992..699e0147 100644
--- a/Proofs/Popcount32.lean
+++ b/Proofs/Popcount32.lean
@@ -70,6 +70,7 @@ def popcount32_program : Program :=
 
 #genStepEqTheorems popcount32_program
 
+set_option trace.simp_mem.info true in
 theorem popcount32_sym_meets_spec (s0 sf : ArmState)
   (h_s0_pc         : read_pc s0 = 0x4005b4#64)
   (h_s0_program    : s0.program = popcount32_program)
@@ -104,6 +105,7 @@ theorem popcount32_sym_meets_spec (s0 sf : ArmState)
     intro n addr h_separate
     simp only [memory_rules] at *
     repeat (simp_mem (config := { useOmegaToClose := false }); sym_aggregate)
+
   done
 
 /--