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