Densitize

Fortunately, the hyperbolicity of the system can be changed by densitizing the lapse and adding constraints to the evolution equations. We densitize the lapse by writing: [...], where [...x] is the densitization parameter, [...]

Just as is done in the NOR system, the standard KST formulation uses a fixed densitized lapse of the form [...]. The reason for this is that by densitizing the lapse we are transforming derivatives of ai into derivatives of dimm.