As a practical matter, it is almost never necessary to refer to +∞ as a sentinel because the right endpoint (and so potentially +∞) in the bracketing range ki ≤ k < ki + 1 will never equal k and so is less interesting in code. However, using both sentinels may make it easier to think about them, and it adds a pleasing symmetry.
This page last modified on 24 January 2006.