Example demonstrating good use of mutual recursion

I would like to know if there is a non-artificial example, where mutual recursion is the most elegant solution to a problem and it cannot be easily reduced/inlined to a single recursive function.

I already know this example (from Wikipedia)

function even?(number : Integer)
    if number == 0 then
        return true
    else
        return odd?(abs(number)-1)

function odd?(number : Integer)
    if number == 0 then
        return false
   else
        return even?(abs(number)-1)

But seriously, no one in their right mind would check the number's parity this way.

I checked the previous answer on this topic here on SO - Are there any example of Mutual recursion? but none of the answers are what I am looking for.

I know it can be useful in recursive parsing - probably the only logical way to implement it, but I need a cleaner, more specific example (preferably a mathematical one).

Thank you for help?

Edit:

Since apparently every tuple of mutually-recursive functions CAN be reduced to a single functions, I would rather want to know if there is a case where use of mutually recursive functions is the best/most readable way.

Mutual recursive code for drawing of Sierpinski curve (and some other curves) looks rather elegant.