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Re: More /.{I->-1} craziness, con brio

• To: mathgroup at smc.vnet.net
• Subject: [mg106636] Re: More /.{I->-1} craziness, con brio
• From: Andrzej Kozlowski <akozlowski at gmail.com>
• Date: Tue, 19 Jan 2010 05:15:06 -0500 (EST)
• References: <200912300915.EAA17299@smc.vnet.net> <hhhmn8$o9t$1@smc.vnet.net> <his71l$lad$1@smc.vnet.net> <201001171213.HAA09349@smc.vnet.net> <hj131g$bdr$1@smc.vnet.net> <4B5489D0.6050602@cs.berkeley.edu>

On 18 Jan 2010, at 17:18, Richard Fateman wrote:

> Andrzej Kozlowski wrote:
>
>> I is never evaluated and is seen as an object with Head Symbol.
>
> Yes, so that explains why the "error" is not caught and the message 
given for that case, too.  In fact the "symbol" is converted to 
something like  I$1234, which was explained in my note. Explaining why a 
system behaves in a certain way is not equivalent to proving that it is 
correct.  At least in my book.

Of course you did not explain anything at all, or rather what you 
explained is wrong. Or perhaps you can explain why there is no renaming 
in the first case but there is in the second:

Trace[With[{I = -I}, 3 + 4 I]]

{With[{I=-I},3+4 I],{{I,I},-I,-I},3+4 (-1) I,{4 (-1) I,-4 I},3-4 I,3-4 I}

Trace[Module[{I = -I}, 3 + 4 I]]

{Module[{I=-I},3+4 I],{{I,I},-I,-I},{I$4671=-I,-I},{{{I$4671,-I},4 (-1) I,-4 I},3-4 I,3-4 I},3-4 I}

Guessing wrongly, particularly when one it is easy to check that the guess is wrong, is not the same as explaining.

• References:
  • Re: More /.{I->-1} craziness, con brio
    • From: Richard Fateman <fateman@cs.berkeley.edu>