[Insight-developers] add operator< and operator> support initk::Index

[Brad King]

Miller, James V (Research) wrote:
> What does it mean for an index to be "less than" another?
> 
> In your code snippet, you are defining to "less than" to be: if any component
> of the index1 is less than that component of index2, then index1 is less than
> index2.  Also, if any component of index1 is greater than that component in 
> index2, then index1 is greater than index2.

Actually it is defining a lexicographic total ordering.  It is not very 
useful geometrically but programatically it is useful for storage and 
searching.

-Brad