[frob]

It's the Revised Revised Revised Revised Revised Revised Revised Report on the Algorithmic Language Scheme, or (Revised)^7 Report on the Algorithmic Language Scheme, or R7RS.

[munificent]

(Because, of course, Scheme folks couldn't resist the urge to use a little recursion in the name of the spec instead of defining it as an iterated series of version numbers.)

[marcus0x62]

But its both. Even if you don’t get the joke, you can pretty easily tell that R4RS, R5RS, RNRS represent an ordered list.