[Maxima-bugs] [ maxima-Bugs-3526606 ] Strange pos/neg/zero behaviour of is().

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Bugs item #3526606, was opened at 2012-05-14 08:24
Message generated for change (Settings changed) made by robert_dodier
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Category: Lisp Core - Assume
Group: None
>Status: Closed
>Resolution: Invalid
Priority: 5
Private: No
Submitted By: Rupert Swarbrick (rswarbrick)
Assigned to: Nobody/Anonymous (nobody)
Summary: Strange pos/neg/zero behaviour of is().

Initial Comment:
Without any assume() calls, Maxima sensibly realizes that it doesn't know the sign of h:

(%i1) is(h>0);
(%o1)                               unknown
(%i2) is(h<0);
(%o2)                               unknown

However, it's certain that h is nonzero?!

(%i3) is(h=0);
(%o3)                                false
(%i4) 


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>Comment By: Robert Dodier (robert_dodier)
Date: 2012-05-16 14:02

Message:
"=" is only syntactic equality; it tests whether the expression on the left
is the same expression as on the right. So is(h=0) => false is the correct
result, because the expression h is not the same expression as 0.

is(equal(h, 0)) => unknown, on the other hand.

Closing this report as invalid.

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