Sign of an Interval

The sign of an interval is only deductible if both infinimum and supremum are of the same sign, this can be represented by the following:

PICT

Figure 1: Example of an unsigned and signed interval

Formally for an interval $X ∈ IR$ that is:

- sgn(X)=sgn(x)⇔ sgn(x)= sgn(x)

Otherwise if the sign of the infinimum and supremum are not equal, the interval $X$ is considered signless.