  We address the problem of testing weak optimality of a given solution of a
given interval linear program. The problem was recently wrongly stated to be
polynomially solvable. We disprove it. We show that the problem is NP-hard in
general. We propose a new algorithm for the problem, based on orthant
decomposition and solving linear systems. Running time of the algorithm is
exponential in the number of equality constraints. Interval linear programs
with inequality constraints only can be processed in polynomial time.
