def _blockedPairs(self, blocks):

        block, blocks = core.peek(blocks)
        self._checkBlock(block)

        combinations = itertools.combinations

        pairs = (combinations(sorted(block), 2) for block in blocks)

        return itertools.chain.from_iterable(pairs)
:returns: A frozenset including one or more of ``'box'``, ``'flow'`` and
dataset/ETHPy150Open datamade/dedupe/dedupe/api.py/DedupeMatching._blockedPairs--crossover with--dataset/ETHPy150Open AnyMesh/anyMesh-Python/example/urwid/widget.py/Widget.sizing