  So to zip two streams s and t one starts with the head of s, and then begins the same process of zipping all over again, but this time with t first and the tail of s second.  For example, if x†, y†, and z† are the solutions to the system in equation (2) above, then we might wish to consider, for example,  zip(x†, y†).   In unraveled form, this is 