abstract DuneSystem
	xor Precon
		SeqGs
		SeqSOR
	xor Solver
		CGSolver
		BiCGSTABSolver
		LoopSolver
		GradientSolver
	pre -> integer
	[pre >= 0]
	[pre <= 6]
	post -> integer
	[post >= 0]
	[post <= 6]
	[pre + post > 0]
	cells -> integer
	[cells >= 50]
	[cells <= 55]
Cp : DuneSystem