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Bug introduced in 10.3.0 and fixed in 10.4.

Consider the following (very simple) graph, with two vertices and one edge:

g = Graph[{1, 2}, {1 <-> 2}];

I can use EdgeDelete to remove the edge from this graph:

EdgeDelete[g, {1 <-> 2}] (* returns Graph[{1, 2}, {}] *)

But something bizarrre happens if I use EdgeDelete to not remove any edges from the graph:

EdgeDelete[g, {}] (* returns StandardForm *)

For some reason, Mathematica returns the symbol StandardForm! To be more precise, it returns some object that appears to be the symbol StandardForm. I say this because attempting to interact with it in any way hangs the kernel:

EdgeDelete[g, {}] // FullForm    (* evaluating any of these three lines *)
Print[EdgeDelete[g, {}]]         (* causes the kernel to hang *)
Evaluate[EdgeDelete[g, {}]]

What's going on here? I'm using Mathematica 10.3 on Windows 10.

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    $\begingroup$ This is a v10.3 regression. I've reported it to WRI as a bug (soon after v10.3 was released) under case number 3449282. $\endgroup$
    – kirma
    Jan 10, 2016 at 14:26
  • $\begingroup$ What happens when you evaluate EdgeDelete[g, {}] followed by evaluating FullForm[Hold @@ %] $\endgroup$
    – Coolwater
    Jan 10, 2016 at 14:28
  • $\begingroup$ @Coolwater After In[391] := EdgeDelete[g, {}], evaluating FullForm[Hold @@ %] produces Hold[391]. For some reason, despite the Mathematica notebook displaying Out[391] := StandardForm, Out[391] remains undefined. $\endgroup$
    – David Zhang
    Jan 10, 2016 at 14:44
  • $\begingroup$ @kirma So, in 10.2 it worked? Can't check it myself as I have removed all minor versions to reclaim space on my HD. If so, could you make an appropriate header as described here? $\endgroup$
    – Sjoerd C. de Vries
    Jan 10, 2016 at 18:49
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    $\begingroup$ @xavier Thanks. Added the bug header. $\endgroup$
    – Sjoerd C. de Vries
    Jan 10, 2016 at 22:19

1 Answer 1

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Bug introduced in 10.3.0 and fixed in 10.4.

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    $\begingroup$ Why is it voted for deletion? This question is unlikely to have any other answer than one like this, so why leave it unanswered? $\endgroup$
    – István Zachar
    Jul 17, 2016 at 8:18

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