The smallest value that is contained here This is an Option, because of cases like ExclusiveUpper(Int.MinValue), which are pathological and equivalent to Empty
Map the Interval with a non-decreasing function.
Map the Interval with a non-decreasing function. If you use a non-monotonic function (like x^2) then the result is meaningless. TODO: It might be good to have types for these properties in algebird.
Iterates all the items in this Upper[T] from highest to lowest