When you see this traffic signal is turned on, you may

a. go straight regardless of other signals
b. turn right without any restrictions
c. turn left if the intersection is clear in your direction
d. yield to traffic

1. define independent-set as the problem that takes a graph g and an integer k and asks whether g contains an independent set of vertices of size k. that is, g contains a set i of vertices of size k such that, for any v and w in i, there is no edge (v,w) in g. show that independent-set is np-complete.