iOverlap (a1, a2, b1, b2)

Write the function iOverlap that tests whether 2 closed intervals overlap. It takes 4 numbers (ints or floats) a1, a2, b1, b2 that describe the two closed intervals [a1,a2] and [b1,b2] of the real number line, and returns True if these two closed intervals overlap (even if at only one point) and False otherwise. If a1>a2 , then the interval [a1,a2] is empty. If b1>b2 , then the interval [b1,b2] is empty. Both intervals are closed, so contain their endpoints. For example, the intervals [1,2] and [2,3] overlap at the point 2.