Special Assignment

interval<T>& set_whole(); 
interval<T>& set_empty(); 
interval<T>& set_lunbound(); 
interval<T>& set_runbound();

These assign special values to the given interval object.

set_whole(): Set the current interval $A ∈ IR$ to an unbounded state $a= -∞$ and $a-=∞$ . Returns a reference to the current object.
set_empty(): Set the current interval $A ∈IR$ to $A = ∅$ . Returns a reference to the current object.
set_lunbound(): Set the infinimum of the current interval as unbounded. Returns a reference to the current object.
set_runbound(): Set the supremum of the current interval as unbounded. Returns a reference to the current object.