Integrability in tetrad formalisms and conservation in cosmology
  Integrability in general tetrad formalisms is reviewed, following and clarifying work of Papapetrou and Edgar. The integrability conditions are (combinations of) the Bianchi equations and their consequences. The introduction of additional constraints is considered. Recent results on the conservation of constraints in the 1+3 covariant formulation of cosmology are shown to follow from the Bianchi equations 
M.A.H. MacCallum