### 9.1 Have You Found a Bug?

If you are not sure whether you have found a bug, here are some guidelines:

- If the assembler gets a fatal signal, for any input whatever, that is a as bug. Reliable assemblers never crash.

- If as produces an error message for valid input, that is a bug.

- If as does not produce an error message for invalid input, that is a bug. However, you should note that your idea of “invalid input” might be our idea of “an extension” or “support for traditional practice”.
- If you are an experienced user of assemblers, your suggestions for improvement of as are welcome in any case.