Cue indirection

In mathematics, the factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n.

fn factorial_recursive(n: u64) -> u64 {
  match n {
      0 => 0,
      _ => n * factorial_recursive(n - 1)
  }
}

DITA

Figure 1. factorial.dita
<p>In mathematics, the factorial of a non-negative integer <i>n</i>,
  denoted by <i>n</i>!, is the product of all positive integers less than or
  equal to <i>n</i>.</p>
<codeblock><coderef href="factorial.txt"/></codeblock>
Figure 2. factorial.txt
fn factorial_recursive(n: u64) -> u64 {
  match n {
      0 => 0,
      _ => n * factorial_recursive(n - 1)
  }
}