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confused about asserting variable is element of Reals

• To: mathgroup at smc.vnet.net
• Subject: [mg103084] confused about asserting variable is element of Reals
• From: dushan <dushanm at spinn.net>
• Date: Mon, 7 Sep 2009 02:36:43 -0400 (EDT)

I'm still learning Mathematica (using 7.0.1) and don't understand
Mathematica's response.  After finally finding out how to assert that a
variable is real, I tried to verify this by asking Mathematica to show me that
it knew the imaginary part of the variable is zero.  But I couldn't
find a way to do that..  Here're my instructions:

    In[1]:=   a (ESC)el(ESC) Reals
    Out[1]:= a (the element-of symbol) Reals

    In[2]:=   ##Im[a]
    Out[2]:= Im[a]

where '##' is any of {null, Refine[, Simplify[, FullSimplify[}.  I
also tried some other combinations, such as 'a^2 - Re[a]^2', but these
didn't help either.

What am I doing wrong?  How do I verify such things?

Thanks.

- Dushan Mitrovich

• Follow-Ups:
  • Re: confused about asserting variable is element of Reals
    • From: Leonid Shifrin <lshifr@gmail.com>
  • Re: confused about asserting variable is element of
    • From: Patrick Scheibe <pscheibe@trm.uni-leipzig.de>