# Can we substitute the term used for the univariate derivative for y'

One new question. I sincerely apologize to use so much the common ressource. This works perfectly

```
x,θ,z = SR.var('x θ z')
y = function('y')
x = function('x')
diff(y(x(θ,z)), z)
```

My question is simply is there a way to substitute $y^\prime(x(\theta,z))$ to $D_0(y(x(\theta,z))$ since $y$ is univariate ? And if this is possible to do the same thing for second order.