+ ##
+ ## INPUTS:
+ ##
+ ## * ``fa`` - The value of `f` at one end of the interval.
+ ##
+ ## * ``fb`` - The value of `f` at the other end of the interval.
+ ##
+ ## OUTPUTS:
+ ##
+ ## * ``has_root`` - True if we can use the I.V.T. to conclude that
+ ## there is a root on [a,b], false otherwise.
+ ##
+