Idiomatic way of writing nested loops?

[Anton Fediushin via Digitalmars-d-learn]

On Monday, 17 July 2017 at 11:32:45 UTC, Sebastiaan Koppe wrote:
> On Monday, 17 July 2017 at 11:07:35 UTC, Anton Fediushin wrote:
>> Hello! What is the best way of rewriting this code in 
>> idiomatic D manner?
>
> https://dlang.org/phobos/std_algorithm_setops.html#.cartesianProduct

Thank you! I knew it is in the library! So, `parallel` will work 
just fine with this function, isn't it?