  In early 1929, V. Fock (initially in collaboration with D. Iwanenko) and H.
Weyl developed independently from each other a general relativistic
generalization of the Dirac equation. In the core, they arrived at the same
theory by the introduction of a local (topologically trivial) spinor structures
and a lifting of the Levi-Civita connection of underlying space-time. They both
observed, in slightly different settings, a characteristic underdetermination
of the spin connection by a complex phase factor, which gave the symbolical
possibility for a reformulation of Weyl's old (1918) idea to characterize the
electromagnetic potential by a differential form transforming as a gauge field.
Weyl and Fock realized the common mathematical core of their respective
approaches in summer 1929, but insisted on differences in perspective. An
interesting difference was discussed by Weyl in his Rouse Ball lecture in
1930,. He contrasted the new type of unification strongly to the earlier
geometrically unified field theories (including his own). He was quite explicit
that he now considered his earlier ideas on geometrization of ``all of
physics'' as premature and declared that the new, more empirically based
approach would have to go a long way before it could be considered as a true
"geometrization" of matter structures.
