The covariant derivative of a Tensor (also called the Semicolon Derivative since its symbol is
a semicolon) is given by
See also Comma Derivative, Connection Coefficient, Covariant Tensor, Divergence
Morse, P. M. and Feshbach, H. Methods of Theoretical Physics, Part I.
New York: McGraw-Hill, pp. 48-50, 1953.