Problem with solve and solve_ineq

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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 $x_1 \leq 20 + 2*x_0$.