  We present observations of the CO(1-0) emission in the central 750 pc (10
arcsec) of the counter-rotating disc galaxy NGC 4550, obtained at the Institut
de Radioastronomie Millimetrique (IRAM) Plateau de Bure Interferometer. Very
little molecular gas is detected, only 1 x 10^7 solar masses, and its
distribution is lopsided, with twice as much molecular gas observed at positive
relative velocities than at negative relative velocities. The velocity gradient
in the CO(1-0) emission shows that the molecular gas rotates like the thicker
of the two stellar discs, which is an unexpected alignment of rotations if the
thinner disc was formed by a major gas accretion event. However, a simulation
shows that the gas rotating like the thicker disc naturally results from the
coplanar merger of two counter-rotating disc galaxies, demonstrating the
feasibility of this scenario for the formation of NGC 4550. We investigate
various star formation tracers to determine whether the molecular gas in NGC
4550 is currently forming stars. UV imaging data and optical absorption
linestrengths both suggest a recent star formation episode; the best-fitting
two population model to the UV-optical colours yields a mass of young stars of
5.9 x 10^7 solar masses with an age of 280 Myr. The best information on the
current star formation rate is a far infrared-based upper limit of only 0.02
solar masses per year. We are thus witnessing NGC 4550 either in a dip within a
bursty star formation period or during a more continuous low-level star
formation episode.
