### 2.54.4 List of variables of an algebraic expressions: `algvar`

`algvar` takes as argument an expression.
`algvar` returns the list of the symbolic variable names used in this expression. The list is ordered by the algebraic extensions required to build the original expression.
Input :

`algvar(y+x*sqrt(z))`

Output :

`[[y,x],[z]]`

Input :

`algvar(y*sqrt(x)*sqrt(z))`

Output :

`[[y],[z],[x]]`

Input :

`algvar(y*sqrt(x*z))`

Output :

`[[y],[x,z]]`

Input :

`algvar(y+x*sqrt(z)+y*sin(x))`

Output :

`[[x,y,sin(x)],[z]]`