I want to do some formal calculus with a unknown functions for the purpose of solving differential equations
Say F(t) = v(t)*t^2, where v is an unknown differentiable function. Then I would like to declare v as such and be able to get
F.diff(t) = 2tv+t^2*v.diff(t)
It is similar to this question, but the solution does not seem to work anymore, as function() takes only one argument and not 2 as in the description; ask.sagemath.org/question/8822/is-there-any-way-to-define-an-as-yet-unknown-function/
Anyone know what the syntax is in 8.9? Or in 9.0, when that becomes available?