Hello,
Using Maxima 5.17.1 with Ecl 8.12.0 I get
the following bizarre behaviour:
(%i1) listify(set_partitions({1,2,3,4},3));
(%o1) [{{1},{2},{3,4}},{{1},{2,3},{4}},{{1},{3},{2,4}},{{1,2},{3},{4}},{{1,3},{2},{4}},
{{1,4},{2},{3}}]
(%i2) listify(set_partitions({1,2,3,4},3))[3];
(%o2) {{1},{3},{2,4}}
(%i3) is(listify(set_partitions({1,2,3,4},3))[3] = {{1},{3},{2,4}});
(%o3) false
There is clearly a bug here. It seems to me that the villain is set_partitions
which doesn't seem to produce "good sets".
Oliver
P.S. It's not just the equality test not working, but e.g.
(%i4) intersection(listify(set_partitions({1,2,3,4},3))[3], {{2},{2,1},{2,3},{2,4}});
(%o4) {}
(%i5) intersection({{1},{3},{2,4}}, {{2},{2,1},{2,3},{2,4}});
(%o5) {{2,4}}