Quiz Yourself on Thinking in Properties

The following property uses a model to validate that it works well. However, the property is failing.

prop_set_union() ->
    ?FORALL({ListA, ListB}, {list(number()), list(number())},
    begin
        SetA = sets:from_list(ListA),
        SetB = sets:from_list(ListB),
        ModelUnion = lists:sort(ListA ++ ListB), 
        lists:sort(sets:to_list(sets:union(SetA, SetB))) =:= ModelUnion
    end).

Is the following statement about the code above true or false?

(True or False) “The problem is with the model. Sets don’t generally allow duplicate elements.”