Safe Haskell | Safe-Infered |
---|

an `Interval`

is a pair of `lower`

and `upper`

,
representing some interval in ordered system.
The lower bound is inclusive and the upper bound is exclusive:
(`lower`

<= x < `upper`

) .
The intersection of two intervals are also interval
but the union of two intervals are not,
so `Interval`

constitute a `PiSystem`

.