Substream applied to unordered streams

[Brian Goetz]

> it seems that 'limit' and 'substream' methods applied to unordered
> stream return result which seems to be only partially deterministic.

Right, which makes sense.  substream (and by extension limit) are 
defined in terms of encounter order; if the encounter order is merely 
accidental, as it is in an unordered stream, there's not much we can do 
there.

> Similar thing is true for 'sorted' method provided stream contains equal
> elements and 'sorted' uses algorithm preserving order.

I think you're asking whether sorting is stable (for ordered streams) or 
not?