Re: Replacement Rule with Sqrt in denominator

*To*: mathgroup at smc.vnet.net*Subject*: [mg114677] Re: Replacement Rule with Sqrt in denominator*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Sun, 12 Dec 2010 05:47:09 -0500 (EST)

On 11 Dec 2010, at 07:52, Jack L Goldberg 1 wrote: > > a) Input as typed: 2<==x<==4. Look at its fullform. On my Mac > running ver. 7 of Mathematica, I get returned, > LessEqual[2,x,4]. > > b) Now type in Reduce[2<==x<==4]. You will get > Inequality[2,LessEqual,x,LessEqual,4]. > > These are are different expressions! How can one program replacement > rules when one can not be sure of the FullForm? These structures are > entirely different. Which fullform can one assume is the one Mathematica sees > in some complicated module wherein one step is a replacement rule? > > Jack Goldberg > Mathematics > University of Michigan > O.K. but I don't see anything here that in any way contradicts anything that has been said about the need for for looking at FullForm before trying pattern matching. Actually, it is als o an argument against using Copy and Paste. To see that, evaluate Reduce[2<==x<==4]. Now, copy the output and paste it into another cell and wrap FullForm around it, then evaluate. You will get LessEqual[2,x,4]. I don't see this as a problem, do you? You can certainly match both forms with a single pattern: {2 <== x <== 4, Reduce[2 <== x <== 4]} /. (a_) <== x <== (b_) | Inequality[a_, LessEqual, x, LessEqual, b_] :> {a, b} {{2, 4}, {2, 4}} Andrzej Kozlowski