On 3/3/12 7:55 PM, AntC wrote:
So is there an arbitrary greek letter term for reordering?
I'm not aware of one, in part no doubt because it's not a semantics-preserving transformation (that is, not in the same sense as that used in defining alpha, beta, eta, delta,...).
In the extension to lambda calculus I presented at NASSLLI a couple years back[1] it is indeed semantics-preserving. In that context I named it chi, because it's a chiastic transformation. Though do note that the calculus also supports an alternative interpretation of reordering, dubbed ksi (for, er, "ksiastic" transformations?). That is, when accounting for reordering we can either reorder the abstractions (chi) or we can reorder the applications (ksi); in many contexts it is impossible to distinguish them on pretheoretical grounds, though there are places where they diverge.
For the record, renaming variables is usually called "alpha-variance" and the alpha-equivalence relation is "modulo alpha-variance". ("Modulus" is a noun; "modulo" is, in English, a preposition.)
[1] http://llama.freegeek.org/~wren/pubs/ccgjp_nasslli2010.pdf -- Live well, ~wren _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
