# How the new version achieves this:diff(x(t)*y(t)) in the latest version?

How the new version achieves this: `diff(x(t)*y(t))`

in the latest version?

```
sage: t = var(’t’)
sage: x = function(’x’, t)
sage: y = function(’y’, t)
sage: diff(x(t)*y(t),t)
TypeError: Substitution using function-call syntax and unnamed arguments
has been removed. You can use named arguments instead, like EXPR(x=..., y=...)
```