def is_valid_trajectory(traj):
    """ Checks if trajectory format is compatible with Cpptraj """
    formats = ('crd', 'cdf', 'netcdf', 'restart', 'ncrestart', 'restartnc',
        'dcd', 'charmm', 'cor', 'pdb', 'mol2', 'trr', 'gro', 'binpos',
        'xtc', 'cif', 'arc', 'sqm', 'sdf', 'conflib')
    return traj in formats
