2.
"Covariance
Properties
of the
Field
Equations
of the
Theory
of Gravitation Based
on
the
Generalized
Theory
of
Relativity"
[Einstein
and
Grossmann
1914b]
Published
29
May
1914
In:
Zeitschrift
für
Mathematik und
Physik
63
(1914):
215-225.