Predicate that returns
True whenever the given pair of points brackets
a root of the given function.
bracket f x1 x2: Given a function and an initial guessed range x1 to x2,
this function expands the range geometrically until a root is bracketed by
the returned values, returning a list of the successively expanded ranges.
The list will be finite if and only if the sequence yields a bracketing pair.
subdivideAndBracket f x1 x2 n: Given a function defined on the interval
[x1,x2], subdivide the interval into n equally spaced segments and search
for zero crossings of the function. The returned list will contain all
bracketing pairs found.