Comment #1 on issue 1928 by basti.kr: Boolean algebra inconsistencies
http://code.google.com/p/sympy/issues/detail?id=1928
> * Equivalent required its arguments to have arithmetic comparison
> defined.
You also changed its behavior.
Before it was:
In [1]: Equivalent(x,x,y)
Out[1]: Equivalent(x, x, y)
Now it gives:
In [10]: Equivalent(x,x,y)
Out[10]: Equivalent(x, y)
Both expressions are equivalent :) but the second is simpler, so I like
it. What I don't understand is how
Equivalent(x) is mathematically defined. Now it gives in sympy:
In [20]: Equivalent(x,x)
Out[20]: Equivalent(x)
Shouldn't this return True instead?
> * To check for that kind of error, tests in test_boolalg.py use
> instances
> of Boolean instead of Symbols.
I don't know if there is a general policy, but I saw at least some tests
where symbols where just defined once globally and not again and again
in every single function.
> * Nand and Nor now call And and Or immediately
Was there some reason why this was written so complicated before? It now
definitely gives the right result and it's much simpler to understand.
And I also think it's faster than before. So imho this is a good change ;)
BTW is there somewhere defined what Nand of more than two elements
gives? In sympy it is NOT(AND(...)) but couldn't it also be defined as
NAND(x,y,z) = NAND(NAND(x,y),z)?
> * Since Or() is False, the correct value for Nor() is True.
> * Xor stops raising an exception with non-Boolean args.
> * Add XOR operator ('^') support for Booleans.
Since this also defines the ^ operator for symbols this is a rather big
change. I'm +0 for it. What do others think?
Also in this commit you have some trailing whitespaces where you change
the gotchas. Since it isn't source code it isn't checked for.
> * Bring test coverage back to 100%
>
Everything else looks fine and ready to push ;)
Sebastian
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