### 5.56.4 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]]