#7805

Fixed the bug by returning False when the method _contains of an Interval gets another Interval
So you want _contains to return False if other is *not* a number? in this case, why not do something like (pseudo code):
if is_symbolic(other):
    Raise Exception #don't know what kind of exception to raise there
if not is_number(other): 
    return False
#verify if other is between start and end as in the code