x1+x2≥1 x1≥1 x1+x2≥1 x,+x,+x1≥1 st x1+x4≥1 x1+x2+x4≥1 12+x4≥1 ①③④⑤⑥⑦⑧9⑩ x2+x1≥1                 s.t. x1 + x4 1 x1 + x2 1 x1 1 x1 + x3 1 x3 1 x1 + x3 + x4 1 x1 + x2 + x4 1 x2 + x4 1 x4 1 x3 + x4 1 1 2 3 4 5 6 7 8 9 10 11