! Desbazeille, Ex. 1.8
max 4x1 + 3x2 - x3 +2x4 +6x5
subject to
a) 3x1 +x3 -x5 = 3
b) -x1 -x2 +3x4 = 12
c)  x2 +x3 +x5 = 4
end