close (OpenGoal (Simple (Lang    _) _) _ ) =
  error "Distribution.Solver.Modular.Dependency.close: called on Lang goal"
close (OpenGoal (Simple (Lang    _) _) _ ) =
  error "Distribution.Solver.Modular.Dependency.close: called on Lang goal"
close (OpenGoal (Simple (Lang    _) _) _ ) =
  error "Distribution.Solver.Modular.Dependency.close: called on Lang goal"