Takes a set of precisely 2 series. Uses the first (set) as the dividend and the second (set) as the divisor to generate a quotient series (i.e. set/set) as the return value.
If at any point in time there are not exactly two points (a dividend and a divisor) nothing is included in the result for that point in time. If the input set to divide() does not contain exactly two series, the return value will be an empty set.