I was trying to put an maximum error finder into my approximate integration program, (Using Simpson's Rule), and I ran into a problem finding the 4th derivative of the function. I tried nesting the "nDeriv()" commands, like so:

`:fMax(abs(nDeriv(nDeriv(nDeriv(nDeriv(Y1,X,X),X,X),X,X),X,X)),X,A,B)`

But it threw an "ILLEGAL NEST" error, because apparently nests more than one level deep with nDeriv() are illegal. I also tried storing each derivative as a new function, like so:

```
:...
:nDeriv(Y1,X,X->Y2
:nDeriv(Y2,X,X->Y3
:nDeriv(Y3,X,X->Y4
:nDeriv(Y4,X,X->Y5
:...
```

But this, for some reason, gave me a data type error, or something similar. I don't quite recall which error it was.

Does anyone know how to get around this? Thanks.