j = Fun $ \ a -> Fun $ \ b -> Fun $ \ c -> Fun $ \ d -> 
    app (app a b) (app (app a d) c)
j = Fun $ \ a -> Fun $ \ b -> Fun $ \ c -> Fun $ \ d -> 
    app (app a b) (app (app a d) c)
j = Fun $ \ a -> Fun $ \ b -> Fun $ \ c -> Fun $ \ d -> 
    app (app a b) (app (app a d) c)