Another crucial general technique required when writing AI programs is search. Often there is no direct way to find a solution to some problem. However, you do know how to generate possibilities. For example, in solving a puzzle you might know all the possible moves, but not the sequence that would lead to a solution. When working out how to get somewhere you might know all the roads/buses/trains, just not the best route to get you to your destination quickly. Developing good ways to search through these possibilities for a good solution is therefore vital. Brute force techniques, where you generate and try out every possible solution may work, but are often very inefficient, as there are just too many possibilities to try. Heuristic techniques are often better, where you only try the options which you think (based on your current best guess) are most likely to lead to a good solution.