1*X4 +1*X5 +1*X6 -1  = 0 
-1*X4 -1*X5  + 1 >= 0
1*X5  >= 0
1*X4  >= 0
1*X3  >= 0
1*X2  >= 0
1*X1 +1*X5 -1 >= 0
1*X1 +1*X2 -1*X4 -1*X5  >= 0
1*X1 +1*X2 +1*X3 -1 >= 0