radoslav hodnicak wrote:
> Ok I know this was debated already here BUT
> 
> VisualWorks ignores nil, VisualAge ignores nil, Dolphin ignores nil,
> ObjectStudio ignores nil, Smalltalk MT ignores nil, Slate ignores nil ...

Maybe better we can say they actually *add* nothing. As far as you're 
adding "nothing" to the set, it stays still the same. It seems logical 
even in Dictionary where "nothing" can *lead* to something or again to 
nothing.

However to other collections like Bag, Array, OrderedCollection you can 
add "nothing" a couple of times and then remove it like it would be a 
thing :)))

-- 
Kamil