diff --git a/haskus-utils-variant.cabal b/haskus-utils-variant.cabal
--- a/haskus-utils-variant.cabal
+++ b/haskus-utils-variant.cabal
@@ -1,6 +1,6 @@
-cabal-version: >=1.20
+cabal-version: 1.20
 name: haskus-utils-variant
-version: 2.0.1
+version: 2.0.2
 license: BSD3
 license-file: LICENSE
 copyright: Sylvain Henry 2018
diff --git a/src/lib/Haskus/Utils/EADT.hs b/src/lib/Haskus/Utils/EADT.hs
--- a/src/lib/Haskus/Utils/EADT.hs
+++ b/src/lib/Haskus/Utils/EADT.hs
@@ -40,6 +40,7 @@
    -- * Extensible ADT
    , EADT
    , (:<:)
+   , (:<<:)
    , pattern VF
    , appendEADT
    , liftEADT
@@ -268,8 +269,14 @@
 -- | An extensible ADT
 type EADT xs = Fix (VariantF xs)
 
+-- | Constructor `f` is in `xs`
 type family f :<: xs where
    f :<: xs = EADTF' f (EADT xs) xs
+
+-- | Forall `x` in `xs`, `x :<: ys`
+type family (:<<:) xs ys :: Constraint where
+   '[] :<<: ys       = ()
+   (x ': xs) :<<: ys = (x :<: ys, xs :<<: ys)
 
 type EADTF' f e cs =
    ( Member' f cs
diff --git a/src/lib/Haskus/Utils/Variant.hs b/src/lib/Haskus/Utils/Variant.hs
--- a/src/lib/Haskus/Utils/Variant.hs
+++ b/src/lib/Haskus/Utils/Variant.hs
@@ -24,6 +24,7 @@
    , pattern V
    , pattern VMaybe
    , (:<)
+   , (:<<)
    , (:<?)
    -- * Operations by index
    , toVariantAt
@@ -100,7 +101,7 @@
 where
 
 import Unsafe.Coerce
-import GHC.Exts (Any)
+import GHC.Exts (Any,Constraint)
 import Data.Typeable
 
 import Haskus.Utils.Monad
@@ -350,6 +351,11 @@
    ( Member x xs
    , x :<? xs
    )
+
+-- | Forall `x` in `xs`, `x :< ys`
+type family (:<<) xs ys :: Constraint where
+   '[] :<< ys       = ()
+   (x ': xs) :<< ys = (x :< ys, xs :<< ys)
 
 -- | A value of type "x" **might** be extracted from (V xs).
 -- We don't check that "x" is in "xs".