max: 2 y1 + 5 y2 - 3 y3;
f1:  4 y1 +   y2 -   y3 <= 30;
f2:    y1 + 5 y2 - 2 y3 <= 40;
f3:    y1 -   y2 + 3 y3  = 12;
f4:         3 y2 + 4 y3 >= 2;

	-inf < y1 <= 0;
//	0 <= y2 < +inf;
	-inf < y3 < +inf;