sympy/sympy — pull request #698 by miham (2011-11-05 12:07:40+00:00)
Title: Fix ode_order (issue 2736).

Before these commits ``ode_order`` incorrectly calculated order for expressions
like ``Derivative(x*f(x), x)``, because it assumed that any derivative is a
derivative of f(x) only, which is ussually not true (in the former example, we
have a derivative of a product, ``x*f(x)``).