Hi,
On Wed, 27 Apr 2011 15:25:18 -0700 (PDT)
tvn <[email protected]> wrote:
> 1) Some expressions are evaluated to be the same
>
> sage: (-x +y == 0) in [x -y == 0]
> True
>
> sage: Set([-x +y > 0,x -y > 0])
> {-x + y > 0}
I don't know exactly what is going wrong here. Both expressions have
the same hash:
sage: var('x,y')
(x, y)
sage: hash(x -y >= 0)
1137549114
sage: hash(y -x >= 0)
1137549114
Then the comparison operator is used. It's likely that each inequality
is seen as False, so we decide that they are equal.
Feel free to open a ticket about this.
> 2) Multiplication on an inequality expression with a negative
> number doesn't change its inequality sign.
>
> sage: -1*(x + y > 0)
> -x - y > 0
>
> For this case I rather Sage crashes or returns I don't know how to do
> this, not implement or whatever than returning the above results.
This is #7660:
http://trac.sagemath.org/sage_trac/ticket/7660
Cheers,
Burcin
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