> For the complete documentation index, see [llms.txt](https://trizen.gitbook.io/sidef-lang/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://trizen.gitbook.io/sidef-lang/programming_tasks/t/topic_variable.md).

# Topic variable

The underscore (\_) topic variable is defined at compile-time in every block of a program. To call a method on it, we can just use the prefix dot (*.*) operator, followed by a method name, which is equivalent with *\_.method*

```ruby
say [9,16,25].map{ .sqrt }   # prints: [3, 4, 5]
```