You will see a sequence of Web pages showing the progress of backtracking for an example Prolog query on an example database. This is a "zigzag diagram" or backtracking chart where each column represents a predicate expression in the query. The entries in the columns show what happens to expressions: "succeeds", "fails", or a list of variable bindings. These diagrams are drawn so that movement is from left to right in each row and backtracking occurs in moving from the end of a line to the next line.