def is_mo_spec(mo):
    """Checks if :literal:`mo` is of :literal:`mo_spec` type. 
  (See :ref:`Central Variables` for details.)"""
    from orbkit.orbitals import MOClass
    if not isinstance(mo, MOClass):
        return False
    return_val = True
    for i in mo:
        try:
            return_val = return_val and 'coeffs' in i.keys()
        except:
            return_val = False
    return return_val
