greetings, I have been using Sage extensively in the past several months
and really like it. Hopefully I can make some contributions to it directly
someday.
Below lists two things about Expression in Sage that are not very intuitive
and should get addressed because it is very error-prone, at least for new
users like myself.
'Sage Version 4.6.2, Release Date: 2011-02-25'
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}
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.
---
I posted this in sage-support but no reply so hopefully will get more
feedbacks here.
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