Programs from Chapter 4 include:

o graph_decls.p		This is Program 4.1, p. 189
o lazy_array.p		This is Program 4.2, p. 192
o bfs.p			This is Program 4.3, p. 195
o dfs.p			This is Program 4.4, p. 197
o topsort.p		This is Program 4.5, p. 217
o strong.p		This is Program 4.6, p. 210-211
o biconnected.p		This is Program 4.7, p. 216-217
o geo_decls.p		This is Program 4.8, p. 220-221
o onsegment.p		This is Program 4.9, p. 222
o intersect.p		This is Program 4.10, p. 223
o intersection.p	This is Program 4.11, p. 230-231
o convex.p		This is Program 4.12, p. 234
o interior.p		This is Program 4.13, p. 236-237
