# symbolic differentiation of unknown function

I want to do some formal calculus with 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) = 2*t*v+t^2*v.diff(t)`

It is similar to Ask Sage question 8822
but the solution does not seem to work anymore, as `function()`

takes
only one argument and not 2 as in the description.

Anyone know what the syntax is in 8.9? Or in 9.0, when that becomes available?

Note: I updated the answer to Ask Sage question 8822.