Comment 2 for bug 980263

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Robert Collins (lifeless) wrote : Re: [Bug 980263] Re: ThreadSafeForwardingResult checks for empty tags incorrectly

That is indeed wrong, but set differencing wouldn't be right either -
if you assume that the sets are disjoint (they always should be) then
a logical or is correct. A set difference would return empty if for
some reason the tags are not disjoint.
>>> set([1]) - set([1])
set([])