To avoid future confusion, let me emphasize that the terminology introduced in Section 4 differs from that of Einstein,
and indeed that of many contemporary accounts. In this review, the requirement that, if
is a solution to the field
equations, then
must also be a solution is called covariance. General covariance is the requirement that
and
represent one and the same physical solution. Another difference is that Section 4 these conditions are formulated
coordinate independently.