### 4.3 Efficiency Tips

How you write your programs can have a large impact on how efficiently the compiled program runs. The most important thing to do, after choosing suitable data structures, is to put the following declaration near the beginning of the file.

    (declare (usual-integrations))

Without this declaration the compiler cannot recognize any of the common operators and compile them efficiently.

The `usual-integrations` declaration is usually sufficient to get good quality compiled code.

If you really need to squeeze more performance out of your code then we hope that you find the following grab-bag of tips, hints and explanations useful.