Pattern Matching with ReplaceRepated Behaving Unexpectedly

*To*: mathgroup at smc.vnet.net*Subject*: [mg128928] Pattern Matching with ReplaceRepated Behaving Unexpectedly*From*: Brentt <brenttnewman at gmail.com>*Date*: Tue, 4 Dec 2012 04:13:50 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net

I'm having trouble understanding how replace repeated works. I have this expression: In[1]:= {u,a, a,v} //. { {p___, x : Longest[(a_) ..], q___} :> {p, a^Length[{x}], q}, {x___, a^2, y___} :> {x, e, y} } What I think should happen here is that {u,a,a,v} should become {u,a^2,v} and then, since ReplaceRepeated should make another pass, {u,a^2,v} should become {u,e,v}. And actually if I break up the replacement rules, and evaluate them one by one, this is precisely what happens. But when I try to put the replacement rules into a list of rules with replace repeated as above it just does the first rule and stops. I.e. it outputs Out[1]:= {u,a^2,v} Strangely if I do In[2]:= % //. { {p___, x : Longest[(a_) ..], q___} :> {p, a^Length[{x}], q}, {x___, a^2, y___} :> {x, e, y} } I get the result I expected ReplaceRepeated to give me before Out[2]:= {u,e,v} I actually thought Replace Repated exists for this very reason, to keep on applying the rules until the rules do not change the output any longer, but it is failing to do that in this case for some reason even though there still seems to be patterns that should be changed? Can anyone tell me what I am missing here? Thank you, any help will be greatly appreciated.

**Follow-Ups**:**Re: Pattern Matching with ReplaceRepated Behaving Unexpectedly***From:*Bob Hanlon <hanlonr357@gmail.com>