If one day you’re finding yourself in need of doing some interval arithmetic in Ada, then you need look no further than Dmitry Kazakov’s Interval Arithmetic for Ada package:
The packages define a logical and interval types. The interval types are obtained through instantiation of the corresponding generic packages. Interval and numeric types can be mixed where the result has mathematical sense.
So if tri-state logic and dimensioned intervals is what you need, then be sure to check out this package. It’s available in 32/64 bit flavors for Fedora and Debian, and of course also as a plain source package. You can read the full release announcement here.