In the following inequation solving
var('x_0 x_1')
s1=solve(x_1 - 2*x_0 <= 20, x_0)
show(s1)
whatever be the variable $x_0$ or $x_1$ the result obtains is a function of $x_1$. So I try to substitute for solve_ineq()
and then have an error. I need a result in the form $x_1 \leq 20 + 2*x_0$.
