Return a combined set of values from the mapping.

    :param mapping: dict, for each key contains a set of entries

    returns a set of combined entries

def _mappingGetValueSet(mapping, keys):
    """Return a combined set of values from the mapping.

    :param mapping: dict, for each key contains a set of entries

    returns a set of combined entries
    """
    setUnion = set()
    for k in keys:
        setUnion = setUnion.union(mapping[k])
    return setUnion