  Novel "quasi two dimensional" typically layered (semi) metals offer a unique
opportunity to control the density and even the topology of the electronic
matter. Along with doping and gate voltage, a robust tuning is achieved by
application of the hydrostatic pressure. In Weyl semi - metals the tilt of the
dispersion relation cones, k , increases with pressure, so that one is able to
reach type II k > 1 starting from the more conventional type I Weyl semi -
metals k < 1. The microscopic theory of such a transition is constructed. It is
found that upon increasing pressure the I to II transition occurs in two
continuous steps. In the first step the cones of opposite chirality coalesce so
that the chiral symmetry is restored, while the second transition to the Fermi
surface extending throughout the Brillouin zone occurs at higher pressures.
Flattening of the band leads to profound changes in Coulomb screening.
Superconductivity observed recently in wide range of pressure and chemical
composition in Weyl semi-metals of both types. The phonon theory of pairing
including the Coulomb repulsion for a layered material is constructed and
applied to recent extensive experiments on HfTe5.
