Hi,
It seems that there is a major bug in new symbolics simplify()
method involving "D" and symbolic function (Sage-4.0.1).
-----------
sage: f(x) = function('f',x)
sage: f(-x).diff(x)
-D[0](f)(-x)
sage: f(-x).diff(x).simplify()
-D[0](f)(x)
-----------
Notice that simplify() causes f(-x) to become f(x).
Also it seems that the order of operands is getting messed up
------------
sage: x,y = var('x,y')
sage: f(x,y) = function('f',x,y)
sage: f(-y,-x).diff(x)
-D[1](f)(-y, -x)
sage: f(-y,-x).diff(x).simplify()
-D[1](f)(x, y)
------------
I suspect that somewhere ".arguments()" method is used
to evaluate the function rather than the ".operands()" method.
Cheers,
Golam
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