After you've implemented the code in sat_solver.rkt,
answer the two questions below.  This portion is
purely bonus worth up to 15% of the assignment;
you do not need to complete this for full credit.

1.) How might you extend this to produce a list of
    all possible soutions, as opposed to one solution?




2.) How might you extend this to produce an efficient
    generator of all solutions?  Each time the generator
    is queried, it should produce a new solution.  Being
    an efficient generator, it should _not_ just simply
    calculate all solutions at once and iterate over
    the precalculated solutions.