4
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Bug introduced in 9.0 or earlier and fixed in 10.4


How can two graphs with zero edges on four vertices, not be isomorphic? What am I missing?

one = Graph[Range[1, 4], {}]
two = EdgeDelete[Graph[Range[1, 4], {1 <-> 2}], {1 <-> 2}]
IsomorphicGraphQ[one, two]

This returns False under Mathematica 10.1.

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    $\begingroup$ It returns True in 11.0.1 $\endgroup$ – Anjan Kumar Feb 18 '17 at 5:59
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    $\begingroup$ Related: mathematica.stackexchange.com/q/88582/12 That other problem is also about the failure to consider empty graphs isomorphic, but that one is present in 10.4 as well. Yours is not present in 10.4. $\endgroup$ – Szabolcs Feb 18 '17 at 9:30
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As Anjan Kumar says this works in 11.0.1, this is probably yet another stupid bug in Mathematica's graph handling. The following works correctly in 10.1:

IsomorphicGraphQ[one, AdjacencyGraph[AdjacencyMatrix[two]]]
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