> ## Documentation Index
> Fetch the complete documentation index at: https://docs.abscissa.eu/llms.txt
> Use this file to discover all available pages before exploring further.

# Type declarations

> Learn how to specify the types of values.

## Usage

Type declarations allows you to specify the types of variables in Mathsys. There are two ways to do so: via annotations or via declarations and definitions.

## Declarations and definitions

You can annotate the type of a variable when declaring or defining it:

```ms3 theme={"dark"}
# Tensor
Tensor v = []

# Infinite
Infinite x = inf

# No type
Any t = x
```

Once a type is assigned to a variable, it cannot be unassigned or changed. See the formal syntax for all type declarations possible.

## Annotations

Annotations let you define the type of a variable without giving it a value. The syntax is as follows:

```ms3 theme={"dark"}
# Annotation
Tensor u, v

# do whatever
u*v
```

## LaTeX

Type declarations and annotations modify LaTeX output with special formatting in order to distinguish types.