reduce!"a+b"(R) syntax question

[Andrew Spott]

On Tuesday, 21 August 2012 at 17:05:46 UTC, Andrew Spott wrote:
> When I'm doing an anonymous function for something like reduce,
> how are the arguments determined?  Is it alphabetical?  Can I 
> use
> any names (reduce!"d-c"(R)?), or are the names defined in the
> function "reduce"?
>
> This syntax isn't really documented at all in the language
> reference, which makes it a little bit of guess work.
>
> -Andrew

Oh, one more question:

does it act like a delegate?

if I do:

int a = 1;
reduce!"d - c - a"(R);

will that use the "a"? or is that out of scope?  If I want to use
external variables, do I have to do something like:

int a = 1;
reduce!((int c, int d) => d - c - a)(R);

instead?