Re: ReplaceAll (/.)

*To*: mathgroup at smc.vnet.net*Subject*: [mg69208] Re: ReplaceAll (/.)*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Fri, 1 Sep 2006 18:41:12 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*References*: <ed9491$tu$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Bruce Colletti wrote: > Re Mathematica 5.2.0.0. > > Why doesn't: > > (a b) /. x_Times -> List @@ x > > return {a,b}? Trace[a*b /. x_Times -> List @@ x] {{{List @@ x, x}, x_Times -> x, x_Times -> x}, a*b /. x_Times -> x, a*b} > My (flawed) reasoning is that a b has form Times[a,b], and so x matches to Times[a,b]. List@@x replaces Times with List to yield List[a,b], or {a,b}...or so it would seem. > > The explanation is somehow linked to the fact that: > > (a b) /. x_Times :> List @@ x > > returns {a,b}, but I don't see why this works but not the above. Trace[a*b /. x_Times :> List @@ x] {{x_Times :> List @@ x, x_Times :> List @@ x}, a*b /. x_Times :> List @@ x, List @@ (a*b), {a, b}} See Section "2.5.8 Immediate and Delayed Definitions" of The Mathematica Book at http://documents.wolfram.com/mathematica/book/section-2.5.8 Regards, Jean-Marc