# Why `unable to convert (sin(h(x)), cos(h(x))) to a symbolic expression`?

```
f(x) = (sin(x), cos(x))
h = function('h', nargs=1)
f(h(x))
```

works fine and produces (sin(h(x)), cos(h(x))). However, if I try to assign that to a function:

```
g(x) = f(h(x))
TypeError: unable to convert (sin(h(x)), cos(h(x))) to a symbolic expression
```

How can I compose functions like this?

symbolic_expression(f(h(x))) fails, but symbolic_expression( (sin(h(x)), cos(h(x))) ) succeeds.

SageMath version 9.1, Release Date: 2020-05-20

Using Python 3.7.3.

Hello! By carefully checking the code for

`symbolic_expression()`

, I can see that the problem actually happens when that command sends its output to`SR`

. Here is a simpler example:If $f$ is a $\mathbb{R}\rightarrow\mathbb{R}$, instead of $\mathbb{R}\rightarrow\mathbb{R}^2$, there is no error message.

I hope this helps to pinpoint the location of the problem!

A similar example, but using vector: