diff --git a/src/Elab/WiredIn.hs b/src/Elab/WiredIn.hs
index 37002e3..f5cfc77 100644
--- a/src/Elab/WiredIn.hs
+++ b/src/Elab/WiredIn.hs
@@ -216,7 +216,7 @@ outS _ _ _ v             = error $ "can't outS " ++ show (prettyTm (quote v))
 comp :: HasCallStack => NFLine -> NFEndp -> Value -> Value -> Value
 comp _a VI1 u _a0 =  u @@ VI1 @@ VItIsOne
 comp a psi@phi u incA0@(compOutS (a @@ VI1) phi (u @@ VI1 @@ VItIsOne) -> a0) =
-  case force $ a @@ VVar (Bound (T.pack "i") (negate 1)) of
+  case force $ a @@ VVar compVar of
     VPi{} ->
       let
         plic i = let VPi p _ _ = force (a @@ i)              in p
@@ -263,9 +263,9 @@ comp a psi@phi u incA0@(compOutS (a @@ VI1) phi (u @@ VI1 @@ VItIsOne) -> a0) =
       in
       let
         base i   = let VGlueTy b _ _ _ = forceAndGlue (fam @@ i) in b
-        phi i    = substitute (Map.singleton (Bound "i" (negate 1)) i) thePhi
-        types i  = substitute (Map.singleton (Bound "i" (negate 1)) i) theTypes @@ VItIsOne
-        equivs i = substitute (Map.singleton (Bound "i" (negate 1)) i) theEquivs
+        phi i    = substitute (Map.singleton compVar i) thePhi
+        types i  = substitute (Map.singleton compVar i) theTypes @@ VItIsOne
+        equivs i = substitute (Map.singleton compVar i) theEquivs
 
         a i u = unglue (base i) (phi i) (types i @@ u) (equivs i) (b @@ i @@ u)
         a0 = unglue (base VI0) (phi VI0) (types VI0) (equivs VI0) b0
@@ -295,7 +295,7 @@ comp a psi@phi u incA0@(compOutS (a @@ VI1) phi (u @@ VI1 @@ VItIsOne) -> a0) =
        in b1
 
     VType -> VGlueTy a0 phi (fun' "is1" \is1 -> u @@ VI1 @@ is1)
-                            (fun' "is1" \_ -> mapVSystem makeEquiv (u @@ VVar (Bound (T.pack "_equivLine_") (negate 3)) @@ VItIsOne))
+                            (fun' "is1" \_ -> mapVSystem makeEquiv (u @@ VVar equivVar @@ VItIsOne))
 
     VNe (HData False _) Seq.Empty -> a0
     VNe (HData False _) args ->
@@ -330,7 +330,6 @@ compHIT _ a phi u a0 = error $ unlines
   , "a0 = " ++ show (prettyTm (quote (zonk a0)))
   ]
 
-
 compConArgs :: Int -> (NFEndp -> Value) -> Value -> Seq.Seq Projection -> NFEndp -> Value -> Seq.Seq Projection
 compConArgs total_args fam = go total_args where
   go _ _ Seq.Empty _ _ = Seq.Empty
@@ -348,14 +347,15 @@ compConArgs total_args fam = go total_args where
   nthArg i (VSystem vs) = VSystem (fmap (nthArg i) vs)
   nthArg i xs = error $ "can't get " ++ show i ++ "th argument of " ++ show (prettyTm (quote xs))
 
-  makeFiller nth (VNe (HData _ (Bound _ (negate -> 10))) args) phi u a0 =
-    fun $ fill (makeDomain args) phi (system \i is1 -> nthArg nth (u @@ i @@ is1) ) a0
+  makeFiller nth (VNe (HData _ n') args) phi u a0
+    | n' == typeArgument =
+      fun $ fill (makeDomain args) phi (system \i is1 -> nthArg nth (u @@ i @@ is1) ) a0
   makeFiller _ _ _ _ a0 = fun (const a0)
 
   makeDomain (PApp _ x Seq.:<| xs) = fun \i -> foldl (\t (~(PApp _ x)) -> t @@ (x @@ i)) (x @@ i) xs
   makeDomain _ = error "somebody smuggled something that smells"
 
-  smuggle x = VNe (HData False (Bound "__comp_con_tyarg" (negate 10))) (Seq.singleton (PApp P.Ex x))
+  smuggle x = VNe (HData False typeArgument) (Seq.singleton (PApp P.Ex x))
 
 compOutS :: HasCallStack => NFSort -> NFEndp -> Value -> Value -> Value
 compOutS a b c d = compOutS a b c (force d) where
@@ -450,7 +450,7 @@ transp line a0 = comp (fun line) VI0 (system \_ _ -> VSystem mempty) (VInc (line
 makeEquiv :: Value -> Value
 makeEquiv argh = VPair f $ fun \y -> VPair (fib y) (fun \u -> p (vProj1 u) (vProj2 u) y)
   where
-    line = fun \i -> substitute (Map.singleton (Bound (T.pack "_equivLine_") (negate 3)) (inot i)) argh
+    line = fun \i -> substitute (Map.singleton equivVar (inot i)) argh
     a = line @@ VI0
     b = line @@ VI1
 
@@ -488,3 +488,13 @@ idEquiv a = VPair idfun idisequiv where
         ielim (fun (const a)) y y (vProj2 u) (iand i j)
 
   id_fiber y = VPair y (VLine a y y (fun (const y)))
+
+-- magic variables (:vomit:)
+compVar :: Name -- direction of composition
+compVar = Bound (T.pack "_comp_dir") (negate 1)
+
+equivVar :: Name --  direction of equivalence
+equivVar = Bound (T.pack "_equiv_dir") (negate 2)
+
+typeArgument :: Name -- marker for type arguments in composition
+typeArgument = Bound (T.pack "_comp_con_tyarg") (negate 3)
\ No newline at end of file