  A quasi-1D superconductor with odd number of Fermi surfaces is expected to
exhibit a nondegenerate Majorana bound state at the Fermi level at its boundary
with an insulator (where the latter could be an actual insulator material or
vacuum, for a terminated sample). Previous explicit theoretical demonstrations
of this property were done for specific microscopic models of the bulk
Hamiltonian and, most importantly, of the boundary. In this work, we
theoretically demonstrate that this property holds for the whole class of
systems, using the symmetry-based formalism of low-energy continuum models and
general boundary conditions. We derive the general form of the Bogoliubov-de
Gennes low-energy Hamiltonian that is subject only to charge-conjugation
symmetry $\mathcal{C}_+$ of the type $\mathcal{C}_+^2=+1$ and a few minimal
assumptions. Crucially, we also derive the most general form of the boundary
conditions describing the boundary with an insulator, subject only to the
fundamental principle of the probability-current conservation and
$\mathcal{C}_+$ symmetry. Such {\em normal-reflection} boundary conditions do
not contain scattering between electrons and holes. We find that for odd number
of Fermi surfaces a Majorana bound state always exists as long as the bulk is
in the gapped superconducting state, irrespective of the parameters of the bulk
Hamiltonian and boundary conditions. Importantly, our general model includes a
possible {\em Fermi-point mismatch}, when the two Fermi points are not at
exactly opposite momenta, which disfavors superconductivity. We find that the
Fermi-point mismatch does {\em not} have a direct destructive effect on the
Majorana bound state, in the sense that once the bulk gap is opened the bound
state is always present.
