# How to install libFES?

I'm trying to solve a system of Boolean Equations using libFES.

The problem is similar to this question

I'm using the sagemath-dev docker image.

```
sage@80a6191bdbeb:~/sage$ sage -version
SageMath version 9.0, Release Date: 2020-01-01
```

The package is not installed by default.

```
sage: from sage.features.fes import LibFES
sage: LibFES().require()
---------------------------------------------------------------------------
FeatureNotPresentError Traceback (most recent call last)
<ipython-input-2-916ca6c4313c> in <module>()
----> 1 LibFES().require()
/home/sage/sage/local/lib/python3.7/site-packages/sage/features/__init__.py in require(self)
189 presence = self.is_present()
190 if not presence:
--> 191 raise FeatureNotPresentError(self, presence.reason, presence.resolution)
192
193 def __repr__(self):
FeatureNotPresentError: sage.libs.fes is not available.
Failed to import `sage.libs.fes`.
To install sage.libs.fes you can try to run 'sage -i fes'.
Further installation instructions might be available at http://www.lifl.fr/~bouillag/fes/.
```

To install the package I ran as recommended `$ sage -i fes`

but this throws an error `Error: package 'fes' not found`

My question is how do I install libFES?

On a side-note, with the package installed, I should be able to do the following as shown in the docs.

```
sage: from sage.doctest.fixtures import reproducible_repr
sage: R.<x,y,z> = BooleanPolynomialRing()
sage: S = Sequence([x*y+z, y*z+x, x+y+z+1])
sage: sol = S.solve(algorithm='exhaustive_search') # optional - FES
sage: print(reproducible_repr(sol)) # optional - FES
[{x: 1, y: 1, z: 1}]
sage: S.subs( sol[0] )
[0, 0, 0]
```