## Can't infer type

```
{-# LANGUAGE RankNTypes, LambdaCase, TypeOperators,
TypeInType, UnicodeSyntax, GADTs #-}
module T11995 where
import Data.Kind
data NP :: forall k. (ĸ → Type) → ([k] → Type) where
Nil :: NP f '[]
(:*) :: f x → NP f xs → NP f (x:xs)
newtype K a b = K a deriving Show
unK (K a) = a
h'collapse :: NP (K a) xs -> [a]
h'collapse = \case
Nil -> []
K x:*xs -> x : h'collapse xs
```

if we replace `xs`

by an underscore:

```
tJN0.hs:13:29-30: error: …
• Could not deduce: (xs :: [ĸ]) ~~ ((':) ĸ x xs :: [ĸ])
from the context: ((k :: *) ~~ (ĸ :: *),
(t :: [k]) ~~ ((':) ĸ x xs :: [ĸ]))
bound by a pattern with constructor:
:* :: forall k (f :: k -> *) (x :: k) (xs :: [k]).
f x -> NP k k f xs -> NP k k f ((':) k x xs),
in a case alternative
at /tmp/tJN0.hs:13:3-9
‘xs’ is a rigid type variable bound by
a pattern with constructor:
:* :: forall k (f :: k -> *) (x :: k) (xs :: [k]).
f x -> NP k k f xs -> NP k k f ((':) k x xs),
in a case alternative
at /tmp/tJN0.hs:13:3
Expected type: NP ĸ k (K ĸ a) t
Actual type: NP ĸ ĸ (K ĸ a) xs
• In the first argument of ‘h'collapse’, namely ‘xs’
In the second argument of ‘(:)’, namely ‘h'collapse xs’
In the expression: x : h'collapse xs
• Relevant bindings include
xs :: NP ĸ ĸ (K ĸ a) xs (bound at /tmp/tJN0.hs:13:8)
h'collapse :: NP ĸ k (K ĸ a) t -> [a] (bound at /tmp/tJN0.hs:11:1)
Compilation failed.
```

Should it not be able to infer that?

The Glorious Glasgow Haskell Compilation System, version 8.1.20160419