Search problems are called nondeterministic because there is no way to determine what is the best step to take next. A1 problems, by their very nature, tend to be nondeterministic. This can be a source of confusion for programmers who are used to deterministic problems. In this section we will try to clear up that confusion.

This section also serves as an example of how higher-order functions can be used to implement general tools that can be specified by passing in specific functions.

Abstractly, a search problem can be characterized by four features:

The start state.

The goal state (or states).