diff --git a/pate.cabal b/pate.cabal
index 141173a0..3802ae35 100644
--- a/pate.cabal
+++ b/pate.cabal
@@ -17,6 +17,9 @@ build-type:          Simple
 extra-source-files:  CHANGELOG.md
                      tools/pate/static/*.css
                      tools/pate/static/*.js
+                     
+if flag(unsafe-operations)
+  cpp-options: -DUNSAFE_OPS
 
 common shared
   build-depends:       base >= 4.10 && < 5,
@@ -154,6 +157,7 @@ library
                        What4.UninterpFns,
                        What4.JSON,
                        Data.Parameterized.SetF,
+                       Data.Parameterized.SetCtx,
                        Pate.SimState,
                        Pate.Equivalence,
                        Pate.Equivalence.Condition,
diff --git a/src/Data/Parameterized/SetCtx.hs b/src/Data/Parameterized/SetCtx.hs
new file mode 100644
index 00000000..e80b1532
--- /dev/null
+++ b/src/Data/Parameterized/SetCtx.hs
@@ -0,0 +1,126 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE PolyKinds #-}
+
+-- | An 'Ctx.Assignment' with distinct elements, providing a reverse map
+--   from elements to indexes
+module Data.Parameterized.SetCtx 
+  ( SetCtx,
+    toAssignment,
+    empty,
+    lookup,
+    adjust,
+    member,
+    lastIndex,
+    size,
+    fromList,
+    insertMaybe
+  ) 
+  where
+
+import           Prelude hiding (lookup)
+import           Data.Parameterized.Classes ( OrdF )
+import           Data.Parameterized.Some (Some(..))
+import qualified Data.Parameterized.Context as Ctx
+import           Data.Parameterized.Map (MapF)
+import qualified Data.Parameterized.Map as MapF
+import Data.Kind (Type)
+import GHC.TypeLits
+
+#ifdef UNSAFE_OPS 
+import Unsafe.Coerce (unsafeCoerce)
+#endif
+
+data SetCtx (f :: k -> Type) (ctx :: Ctx.Ctx k) =
+  -- the map is maintained as a bijection, so we can recover an 'Ctx.Assignment'
+  -- by sorting the elements based on the index
+  SetCtx { size :: Ctx.Size ctx, _map :: (MapF f (Ctx.Index ctx)) }
+
+asnFromMap :: forall ctx f. Ctx.Size ctx -> MapF (Ctx.Index ctx) f -> Maybe (Ctx.Assignment f ctx)
+#ifdef UNSAFE_OPS
+-- if we sort the contents by their index, the result should be a list of elements in
+-- order according to 'ctx'
+asnFromMap sz m 
+  | MapF.size m == Ctx.sizeInt sz
+  , es <- MapF.toAscList m
+  , Some (ls :: Ctx.Assignment f ctx') <- Ctx.fromList $ (map (\(MapF.Pair _ a) -> Some a) es)
+  = Just (unsafeCoerce ls)
+asnFromMap _ _ = Nothing
+#else
+asnFromMap sz m =
+  Ctx.generateM sz $ \idx -> 
+    case MapF.lookup idx m of
+      Just a -> return a
+      Nothing -> fail "asnFromCompleteMap: incomplete indexes"
+#endif
+
+toAssignment :: SetCtx f ctx -> Ctx.Assignment f ctx
+toAssignment (SetCtx sz m) = 
+    let elems = MapF.fromList $ map (\(MapF.Pair e idx) -> (MapF.Pair idx e)) (MapF.toList m)
+    in case asnFromMap sz elems of
+        Just asn -> asn
+        Nothing -> error "toAssignment: unexpected incomplete indexes"
+
+empty :: SetCtx f Ctx.EmptyCtx
+empty = SetCtx Ctx.zeroSize MapF.empty 
+
+coerceMap :: forall f ctx tp. MapF f (Ctx.Index ctx) -> MapF f (Ctx.Index (ctx Ctx.::> tp))
+coerceMap m =
+#ifdef UNSAFE_OPS 
+  unsafeCoerce m
+#else
+  MapF.map Ctx.skipIndex m
+#endif
+
+member :: OrdF f => f tp -> SetCtx f ctx -> Bool
+member e (SetCtx _ m) = MapF.member e m
+
+lookup :: OrdF f => f tp -> SetCtx f ctx -> Maybe (Ctx.Index ctx tp)
+lookup e (SetCtx _ m) = MapF.lookup e m
+
+-- | NB: This is unsafe to export because there is no guarantee that the provided element
+--   isn't already in the underlying assignment
+append :: OrdF f => f tp -> SetCtx f ctx -> SetCtx f (ctx Ctx.::> tp)
+append e (SetCtx sz m) = 
+  let idx = Ctx.nextIndex sz
+  in (SetCtx (Ctx.incSize sz) (MapF.insert e idx (coerceMap m)))
+
+insertMaybe ::
+  OrdF f => 
+  f tp ->
+  SetCtx f ctx ->
+  Either (Ctx.Index ctx tp) (SetCtx f (ctx Ctx.::> tp))
+insertMaybe e idx_asn = case lookup e idx_asn of
+  Just idx -> Left idx
+  Nothing -> Right (append e idx_asn)
+
+
+adjust ::
+  forall f tp ctx a.
+  OrdF f => 
+  f tp ->
+  SetCtx f ctx ->
+  (forall ctx'. (Ctx.KnownContext ctx', Ctx.CtxSize ctx' <= 1) => 
+    Ctx.Index (ctx Ctx.<+> ctx') tp -> SetCtx f (ctx Ctx.<+> ctx') -> a) ->
+  a
+adjust e idx_asn f = case insertMaybe e idx_asn of
+  Left idx -> f @Ctx.EmptyCtx idx idx_asn
+  Right idx_asn' -> f @(Ctx.SingleCtx tp) (lastIndex idx_asn') idx_asn'
+
+fromList :: forall f. OrdF f => [Some f] -> Some (SetCtx f)
+fromList es_outer = go es_outer empty
+    where
+        go :: forall ctx. [Some f] -> SetCtx f ctx -> Some (SetCtx f)
+        go (Some e: es) idxasn = case insertMaybe e idxasn of
+            Left{} -> Some idxasn
+            Right idxasn' -> go es idxasn'
+        go [] idxasn = Some idxasn
+
+lastIndex :: SetCtx f (ctx Ctx.::> tp) -> Ctx.Index (ctx Ctx.::> tp) tp
+lastIndex (SetCtx sz _) = Ctx.lastIndex sz
\ No newline at end of file