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IsAcyclicDigraph producing errors when digraph is not outputted first #900
Description
The following function generates a digraph which is claimed to not be acyclic if it has not been printed to terminal.
StarDigraphReverse := function(n)
return Digraph (Concatenation ([[2 .. n]], List([1 .. n-1], i -> [] ) ) );
end;
The issue is shown below
gap> IsAcyclicDigraph(StarDigraphReverse(3));
false
gap> StarDigraphReverse(3);
<immutable digraph with 3 vertices, 2 edges>
gap> IsAcyclicDigraph(last);
true
The issue appears to occur for all values of n at least 2.
Activity
[-]IsAcyclicDigraph producing errors when digraph is not outputted first[/-][+]`IsAcyclicDigraph` producing errors when digraph is not outputted first[/+]reiniscirpons commentedon Feb 25, 2026
We tracked it down at the meeting, it seems the issue is the range constructor. Essentially culprit is the
FuncIS_ACYCLIC_DIGRAPHfunction assuming that the underlying lists are all plain lists, and ranges are not like this.Minimal failing example:
Should be fixed by #901 .
reiniscirpons commentedon Feb 28, 2026
Resolved by #901