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However, a few new twists were added to the 1995 competition. First, a complete topological map of the environment was not available. Instead, a set of instructions, for example, "turn third left" and "go past foyer," would guide the robot through the hallways toward a goal room. Second, it would be possible that the instructions contained an error, such as directing the robot toward a nonexistent hallway or room. Third, the information provided in the instructions only specified a number of "openings" that had to be detected before turning into another hallway or entering the goal room. Only the nature of the last opening of every instruction could be inferred (a hallway in the case of a turn instruction or a doorway in the case of an enter instruction), but the intermediate openings could be of any type. The lack of a more qualitative description of the environment limited the capabilities of the probabilistic navigation algorithm on the robot, which could only be used as a sophisticated feature counter (figure 1).