This might be a different problem. Shouldn't this give a syntax
sage: h(x,y) = x+y
y + 3
??? I thought the whole *point* of the h(x,y) notation was to specify
the order - but then you'd figure it would also specify the number of
entries. I guess this is a shorthand, perhaps, but then I don't know
how to get just h(,3) (which is naturally an error), which you'd want
by symmetry. I guess h(x,3) works, but then we should (perhaps?)
require h(3,y) as well?
But in definite integrals the variable of integration is a dummy one
and does not exist out of the integral!
So what happens in a case like this?
Does the result become a function
(x,z) |--> whatever?
I can see it making sense, but I can also see it causing problems.
I was thinking of confusion for the user, because the user has to be
more careful about how they call the function because the arguments
change. Now, this can be alleviated by the user using keyword
arguments, or paying attention and being aware of integration removing a
variable. Again, I don't think this is insurmountable, and arguably
it's desirable to make the user think about how the function domain is
changing, but I feel obligated to bring up the issue as a point against
changing things in a backwards-incompatible way.
I think you have a pretty convincing argument for changing this. +1 to
opening the ticket and changing it.