The `is` sub uses `eq` operator for comparison, which coerces items to Str.
So this ticket comes down to whether or not .Str on sets should sort their
elements. The problem with that is sets can contain different types of objects.
You could further put the argument that .Strs (or .gists) of those objects
should be used and sorted, but that still leaves the issue of two differing
sets producing the same .Str result:
$ 6 'class Bar { method gist { "Foo" } }; say set Bar; say set "Foo"'
set(Foo)
set(Foo)
Thus, I'm closing this ticket, as it appears `is` sub is simply not an
appropriate way to compare two sets.
