Write a pure function cycle-streams that takes streams, xs and ys, and returns a stream. The streams may or may not be the same length, and either one may be infinite, but you may assume they are both non-empty. The elements produced by the stream are pairs where the first part is from xs and the second part is from ys. The stream returned by cycle-streams cycles forever through the streams xs and ys. A constant-time ( O ( 1 ) O(1)) solution is possible.