[Maxima-bugs] [ maxima-Bugs-3477006 ] fact that cannot be forgotten

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Bugs item #3477006, was opened at 2012-01-21 06:21
Message generated for change (Settings changed) made by macrakis
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>Category: Lisp Core - Assume
Group: None
Status: Closed
Resolution: Invalid
Priority: 5
Private: No
Submitted By: Barton Willis (willisbl)
Assigned to: Nobody/Anonymous (nobody)
Summary: fact that cannot be forgotten

Initial Comment:
(%i1) fct : notequal(-(%i*(x-%i))/(2*(1-%i*(x-%i))),0);
(%o1) notequal(-(%i*(x-%i))/(2*(1-%i*(x-%i))),0)

(%i2) assume(fct);
(%o2) [redundant]

(%i3) forget(fct);
sign: argument cannot be imaginary; found %i
 -- an error. To debug this try: debugmode(true);


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Comment By: Stavros Macrakis (macrakis)
Date: 2012-01-26 13:56

Message:
The fact cannot be forgotten because it was never added to the database, as
indicated by "redundant".  A simpler example:

assume(notequal(x,%i)) => [redundant]  <<< i.e. Maxima already knows that x
<> %i
facts() => []    <<< since assumption is redundant, it is not added to DB

The 'assume' system only works for reals (though of course equality and
inequality are well-defined for complexes) and assumes that all variables
are real.  Thus:

<fresh Maxima>
is(equal(x,2)) => unknown
is(equal(x,%i)) => false
is(notequal(y,%i)) => true

Still, I would recommend that instead of simply returning 'redundant' for
declarations involving complexes, that Maxima give a warning message.

             -s

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