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Re: Full simplify problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg122280] Re: Full simplify problem
  • From: dimitris <dimmechan at yahoo.com>
  • Date: Sun, 23 Oct 2011 06:24:23 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <j7u59t$u$1@smc.vnet.net>

On Oct 22, 1:18 pm, "A. Lapraitis" <ffcita... at gmail.com> wrote:
> Hello,
>
> Could anyone explain why the following does not give zero?
>
> In[72]:= Assuming[
>  x == y + z,
>  FullSimplify[
>   E^x - E^(y + z)
>   ]
>  ]
>
> Out[72]= E^x - E^(y + z)
>
> Thanks!

Hello again.

Apart from my original reply I would also like to add the following
attempt which generates a message but
does what you wanted.

Assuming[x === y + z, FullSimplify[E^x - E^(y + z)]]
$Assumptions::fas:Warning: One or more assumptions evaluated to False.
0

?===
lhs === rhs yields True if the expression lhs is identical to rhs, and
yields \
False otherwise.

But I do consider my first attempt the best one (and I finally
understood that this is a normal behavior of FullSimplify thanks to
Mr  Kozlowski).

Dimitris



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