'If ``key`` is in ``dictionary``, set the new value of ``key``
to be the union between the old value and ``value``.
Otherwise, set the value of ``key`` to ``value.
Returns ``True`` if the key already was in the dictionary and
``False`` otherwise.'

@staticmethod
def _set_dict_union(dictionary, key, value):

    if (key in dictionary):
        dictionary[key] = (dictionary[key] | value)
        return True
    else:
        dictionary[key] = value
        return False
