Re: Replacement Rule with Sqrt in denominator

*To*: mathgroup at smc.vnet.net*Subject*: [mg114595] Re: Replacement Rule with Sqrt in denominator*From*: Sebastian <sebhofer at gmail.com>*Date*: Thu, 9 Dec 2010 06:03:04 -0500 (EST)*References*: <idnqpr$q58$1@smc.vnet.net>

I don't want to claim that pattern matching in Mathematica is bugged, I am certainly not entitled to do so. I was always quite happy to follow the rules and look at the FullForm in order to create the correct pattern, until I learned (actually just by following this thread) that this does not always produce the expected results. So even though this may not be a bug, pattern matching can be very confusing sometimes, and, in terms of usability, may seem to be poorly implemented to some people. Having said that, could somebody give me a little insight on how pattern matching "really" works (I'm sure Daniel has done so many times already, please feel free to refer me to previous posts!): What set (or class) of expressions does pattern matching exclude from its "normal" behavior (obviously there is Rational, Complex, whatnot...)? Why? Are there different such classes? Why does 3/5[[1]] fail (alternatively: Why does Rational behave differently then List, say)? TIA Sebastian