Existence, uniqueness and other properties of the BCT (minimal strain   lapse and shift) gauge
  Brady, Creighton and Thorne have proposed a choice of the lapse and shift for numerical evolutions in general relativity that extremizes a measure of the rate of change of the three-metric (BCT gauge). We investigate existence and uniqueness of this gauge, and comment on its use in numerical time evolutions. 
David Garfinkle, Carsten Gundlach, James Isenberg and Niall OMurchadha