kill(all)$

van=facebook.com/LearningCalculus$

load(solve_rec)$

foo: u[n+1] = a*u[n]+b;

solve_rec(foo,u[n],u[0]=1);

solve_rec(foo,u[n],u[0]=1);

f(x):=subst(x,n,rhs(solve_rec(foo,u[n],u[0]=1)))$

f(x);