Question about breadth-first completeness vs depth-first incompleteness

Question

According to Norvig in AIMA (Artificial Intelligence: A modern approach), the Depth-first algorithm is not complete (will not always produce a solution) because there are ca

Answer 1

The properties of depth-first search depend strongly on whether the graph-search or tree-search version is used. The graph-search version, which avoids repeated states and redundant paths, is complete in finite state spaces because it will eventually expand every node. The tree-search version, on the other hand, is not complete—for example, in Figure 3.6 the algorithm will follow the Arad–Sibiu–Arad–Sibiu loop forever

Source: AI: a modern approach