I computed a variational derivative and arrived to the following expression:

∫(4d*{t}(d*{t x}(u)) d*{x}(p) d*{t x}(u) e{p}-4d*{t}(p) d*{x}(d*{t x}(u)) d*{t x}(u) e{p} + 4d*{t}(p) d*{t x}(u) d*{t x x}(u) e{p}-4d*{x}(p) d*{t x}(u) d*{t t x}(u) e{p}}

Here

```
{x,y,z,t}::Coordinate.
d{#}::PartialDerivative.
{x,y,t,u,p,q}::Depends(d{#}).
e{#}::Accent.
```

This expression equals zero. Is there any way to simplify it have zero explicitly?

If I copy the expression and put it to cadabra

```
ex:=4d_{t}(d_{t x}(u)) d_{x}(p) d_{t x}(u) e{p}
-4d_{t}(p) d_{x}(d_{t x}(u)) d_{t x}(u) e{p}
+ 4d_{t}(p) d_{t x}(u) d_{t x x}(u) e{p}
-4d_{x}(p) d_{t x}(u) d_{t t x}(u) e{p};
```

it automatically convert d*{x}(d*{t x}(u)) to d_{t x x}(u). But how to do this with a command?