[Maxima-bugs] [ maxima-Bugs-1318843 ] assume failure to deduce, and consequent infinite looping

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Bugs item #1318843, was opened at 2005-10-08 14:52
Message generated for change (Settings changed) made by robert_dodier
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>Category: Lisp Core - Assume
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Robert Dodier (robert_dodier)
Assigned to: Nobody/Anonymous (nobody)
Summary: assume failure to deduce, and consequent infinite looping

Initial Comment:
assume (a > 0, b > 0, c > 0, d > 0);
assume (c*s + d < 0);
assume (equal (c*r + d, 0));

At this point, r = -d/c and s < -d/c, so s < r.
However, 

integrate ((a*x+b)/(c*x+d), x, r, s);

  =>  Is  s - r  positive, negative, or zero?

response: n;  =>  a solution

response: p; or z;  => somebody calls ASKSIGN1 over and
over

  1> (ASKSIGN1
         ((MPLUS SIMP) ((MTIMES SIMP RATSIMP) -1 $D)
          ((MTIMES SIMP RATSIMP) -1 $C $R)))
  <1 (ASKSIGN1 $ZERO)
  1> (ASKSIGN1 ((MPLUS SIMP) $D ((MTIMES SIMP RATSIMP)
$C $R)))
  <1 (ASKSIGN1 $ZERO)
  1> (ASKSIGN1
         ((MPLUS SIMP) ((MTIMES SIMP RATSIMP) -1 $D)
          ((MTIMES SIMP RATSIMP) -1 $C $R)))
  <1 (ASKSIGN1 $ZERO)
  1> (ASKSIGN1 ((MPLUS SIMP) $D ((MTIMES SIMP RATSIMP)
$C $R)))
  <1 (ASKSIGN1 $ZERO)

etc etc indefinitely.

There are at least 2 problems here.

(1) ASKSIGN failed to determine that s < r and
therefore there is no need for asking about it.

(2) If the response implies something inconsistent with
the facts assumed thus far, something (maybe ASKSIGN)
goes nuts.

I'm inclined to think (2) is more serious. Whatever the
limitations of the assume mechanism to derive stuff
from facts, it shouldn't freak out under any circumstances.

Problem verified in 5.9.0 on Allegro CL 6.2, and
5.9.1.9rc4 on GCL 2.6.7.

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