Should setDifference take a SortedRange?

[Jesse Phillips]

The documentation states:

"The two ranges are assumed to be sorted by less."

Would it make more sense for this function, and its siblings, to 
take a SortedRange instead. This would be a breaking change as it 
would require people to either sort or assumeSorted before 
calling.

But SortedRange was added for exactly this application (I 
believe).