  Geometrical tools, used in Einstein's general relativity (GR), are applied to
dynamo theory, in order to obtain fast dynamo action bounds to magnetic energy,
from Killing symmetries in Ricci flows. Magnetic field is shown to be the shear
flow tensor eigendirection, in the case of marginal dynamos. Killing symmetries
of the Riemann metric, bounded by Einstein space, allows us to reduce the
computations. Techniques used are similar to those strain decomposition of the
flow in Sobolev space, recently used by Nu\~nez [JMP \textbf{43} (2002)] to
place bounds in the magnetic energy in the case of hydromagnetic dynamos with
plasma resistivity. Contrary to Nu\~nez case, we assume that the dynamos are
kinematic, and the velocity flow gradient is decomposed into expansion, shear
and twist. The effective twist vanishes by considering that the frame vorticity
coincides with Ricci rotation coefficients. Eigenvalues are here Lyapunov
exponents. In analogy to GR, where curvature plays the role of gravity, here
Ricci curvature seems to play the role of diffusion.
