### TAU-INTERVAL-LO

access the lower bound of a tau interval
Major Section: TAU-SYSTEM

It is the case that

(tau-interval-lo (make-tau-interval dom lo-rel lo hi-rel hi)) = lo

For a well-formed interval, `lo`

is either `nil`

, denoting negative
infinity, or a rational number giving the lower bound of the interval.
It must be the case that the lower bound is weakly below the upper bound
of a well-formed interval.

When the domain of an interval is `INTEGERP`

, there are additional
constraints on the other components. See make-tau-interval.