Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the well formulation of the Initial Value Problem of metric--affine
  $f(R)$-gravity   We study the well formulation of the initial value problem of f(R)-gravity in
the metric-affine formalism. The problem is discussed in vacuo and in presence
of perfect-fluid matter, Klein-Gordon and Yang-Mills fields. Adopting Gaussian
normal coordinates, it can be shown that the problem is always well-formulated.
Our results refute some criticisms to the viability of f(R)-gravity recently
appeared in literature.

24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
2
The categories of this paper are: math
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
29
The categories of this paper are: funct-an
11
The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
12
The categories of this paper are: nucl-th
19
The categories of this paper are: eess
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph