Generalization for type T being dense

[nji9nji9]

Very useful indeed!

Still I wonder if that could be generalized to better match the mathematical needs:
Interval borders being closed or open.
Actually one has to decide whether borders are all closed or all open (MERGE_TOUCHING)
As kind of syntactical mean for not-dense (integral) types T.

If for every element of type T you can tell the nearest smaller/ larger element
(i.e. T is not dense), you can take that for defining an open interval border.
(E.g. for C floating points: std::nextafter())
But if T doesn't provide an implementation of nextafter()...

Do you think you might generalize in that way?
(The MERGE_TOUCHING thing will be obsolet then).