@article {14140,
	title = {Block preconditioners based on approximate commutators},
	journal = {SIAM Journal on Scientific Computing},
	volume = {27},
	year = {2006},
	month = {2006///},
	pages = {1651 - 1668},
	author = {Elman, Howard and Howle, V. E and Shadid, J. and Shuttleworth, R. and Tuminaro, R.}
}
