def get_parent(vmfs):
    """ From a set of VMFs, determines which one has the lowest map version 
    number, and is therefore the parent.
    
    """
    
    # This avoids the need to subscript and slice.
    vmfs = iter(vmfs)
    
    parent = next(vmfs)
    lowestRevision = parent.revision
    
    for vmf in vmfs:
        revision = vmf.revision
        if revision < lowestRevision:
            parent = vmf
            lowestRevision = revision
            
    return parent