  It is usually assumed that the Bose crystal at $T=0$ corresponds to the
genuine ground state of a Bose system, i.e., this state is non-degenerate and
is described by the wave function without nodes. By means of symmetry analysis
we show that the ground state of a Bose system of any density should correspond
to a liquid or gas, but not to a crystal. The main point is that any
anisotropic state of a system of spinless bosons is degenerate. We prove this
for an infinite three-dimensional (3D) system and a finite ball-shaped 3D
system. One can expect that it is true also for a finite system of any form.
Therefore, the anisotropic state cannot be the genuine ground state. Hence, a
zero-temperature natural 3D crystal should correspond to an excited state of a
Bose system. The wave function $\Psi^{c}_{0}$ of a zero-temperature 3D Bose
crystal is proposed for zero boundary conditions. Apparently, such
$\Psi^{c}_{0}$ corresponds to a local minimum of energy (absolute minimum
corresponds to a liquid). Those properties yield the possibility of existence
of superfluid liquid H$_{2}$, Ne, Ar, and other inert elements. We propose
several possible experimental ways of obtaining them.
