* #variable= 6 #constraint= 3 #product= 9 sizeproduct= 18
*
* Factorization problem: find the smallest P such that P*Q=N
* P is a 3 bits number (x3 x2 x1)
* Q is a 3 bits number (x6 x5 x4)
* N=35
*
* minimize the value of P
min: +1 x1 +2 x2 +4 x3 ;
* P>=2 (to avoid trivial factorization)
+1 x1 +2 x2 +4 x3 >= 2 ;
* Q>=2 (to avoid trivial factorization)
+1 x4 +2 x5 +4 x6 >= 2 ;
* P*Q=N
+1 x1 x4 +2 x1 x5 +4 x1 x6 +2 x2 x4 +4 x2 x5 +8 x2 x6 +4 x3 x4 +8 x3 x5 +16 x3 x6 = 35;