Second and higher derivatives of the metric tensor 
need not be continuous across a surface of discontinuity, but 
and 
must be continuous across it.
Lichnerowicz Conditions
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Cite this as:
Weisstein, Eric W. "Lichnerowicz Conditions." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/LichnerowiczConditions.html