Conventions used in this Manual

We use some conventions in this manual.

For some procedures, notably type predicates, we use iff to mean `if and only if'. The construct is usually something like: `Return val iff condition', where val is usually `#t' or `non-#f'. This typically means that val is returned if condition holds, and that `#f' is returned otherwise.
In examples and procedure descriptions and all other places where the evaluation of Scheme expression is shown, we use some notation for denoting the output and evaluation results of expressions. The symbol => is used to tell which value is returned by an evaluation:
```
(+ 1 2)
=>
3
```
Some procedures produce some output besides returning a value. This is denoted by the symbol -|.
```
(begin (display 1) (newline) 'hooray)
-| 1
=>
hooray
```

@unnumbered{Part I: Introduction to Guile}