In optimization problem, I have two constraints for decision variables $x_1$ and $x_2$ as follow
$0 \leq x_1 \leq u_1$ and $0 \leq x_2 \leq u_2$
I was wondering how can I replace these 2 constraints with just one constraint in terms of $x_1,x_2,u_1,u_2$. Hence, the goal is to reduce the number of constraints. I dont care if this results in nonlinear constraints.