  The nucleus of the box-shaped galaxy NGC4013 has been observed with the IRAM
interferometer in the J=1-0 and J=2-1 lines of 12CO. Our maps show the
existence of a fast--rotating(130 km/s) molecular gas disk of radius r=110pc.
Several arguments support the existence of a bar potential in NGC4013. The
figure-of-eight pattern of the major axis p-v plot, the ring-like distribution
of gas, and the existence of gas emission at non-circular velocities are best
accounted by a bar. We have also detected gas at high z distances from the
plane (z=200-300pc). The latter component is related to a system of 4 Halpha
filaments of diffuse ionized gas that come out from the nucleus. The galactic
fountain model seems the best to account for the Halpha and CO filaments.
Although the peanut distortion can be spontaneously formed by a stellar bar in
the disk, gas at high z might have been ejected after a nuclear starburst. The
Halpha filaments start in the plane of the disk at r=200pc, and reach several
Kpc height at r=600pc, coinciding with the maximum peanut distortion. Although
a link between the bar and the box-shaped bulge in NGC4013 is suggested we find
noticeable differences between the results of previous numerical simulations
and the present observations. The discrepancy concerns the parameters of the
bar generating the peanut. We see in NGC4013 the existence of a strong ILR
region. The inclusion of a dissipative component, which remains to be
thoroughly studied, may change the evolution of the stellar peanut: although in
simulations the peanut appears initially near a marginal ILR, the inflow of gas
driven by the bar, can make two ILRs appear.
