### Differential of a integral?

So I'm trying to calculate the frenet thrihedrom in the "clasic" way, (doing an arc length and his integrals)
but sage don't let me do a diff of a integral. Here ismy code:

```
var('t, n')
assume(n > 0)
c=vector((t,t**2,t**3))
l=sqrt(1+4*t*t+9*t**4)
L= l.integral(t, 0, n)
C=vector((t/L,(t/L)**2,(t/L)**3))
T=C.diff(t)
```

I get this error:

```
AttributeError: 'sage.rings.rational.Rational' object has no attribute 'diff'
```

Any idea of how to do a Diff of a integral?