Stable Numerics Subroutine Library
Programming Reference Manual
Version 1.1 DD-00006-011

3.1.5 Normalized Interval

An interval X ∈IR  is considered to be normalized if either   -
x≤x or a singleton    -
x =x =∅  otherwise the interval is considered to be denormalized in the first case, in the second case if one of but not both of x or -
x are ∅  the interval is considered improper. Singleton intervals are always considered normalized.