def convert_sed_cols(tab):
    """Cast SED column names to lowercase."""
    # Update Column names
    for colname in list(tab.columns.keys()):

        newname = colname.lower()
        newname = newname.replace('dfde', 'dnde')

        if tab.columns[colname].name == newname:
            continue

        tab.columns[colname].name = newname

    return tab