> ## 1 Introduction

> ### 1.1 Purpose

> This reference manual describes the Erlang programming language. The focus is on the language itself, not the implementation. The language constructs are described in text and with examples rather than formally specified, with the intention to make the manual more readable. The manual is not intended as a tutorial.

> Many references are made to built-in functions, BIFs. For a complete list of BIFs, their arguments and return values, refer to `erlang(3)`.

> For documentation about this implementation of Erlang, please refer to ERTS User's Guide.

> ### 1.2 Prerequisites

> It is assumed that the reader has done some programming and is familiar with concepts such as data types and programming language syntax.

> ### 1.3 Document Conventions

> In the document, the following terminology is used:

> - A sequence is one or more items. For example, a clause body consists of a sequence of expressions. This means that there must be at least one expression.
> - A list is any number of items. For example, an argument list can consist of zero, one or more arguments.

> If a feature has been added recently, in Erlang 5.0/OTP R7 or later, this is mentioned in the text.

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