The IA, for example, can be seen as referring to the singleton set {r} that contains the target r and nothing else.
if in line 1 (Figure 2), {r} is replaced by an arbitrary set S, and line 3 is modified as saying C ← D − S instead of C ← D − {r}, then the algorithm produces a description that applies to all elements of S. it is easy enough to let these algorithms produce expressions like "the men" or "the t-shirt wearers," to identify {d 1 , d 3 } and {d 2 , d 3 }, respectively.