!Keyword: transportation, equilibria;
MIN 20 AB2 + 30 AB3 + 40 AB4 + 52 AC2 + 53 AC3 + 54 AC4 + 12 BC2
  + 13 BC3 + 14 BC4 + 52 BD2 + 53 BD3 + 54 BD4 + 20 CD2 + 30 CD3
  + 40 CD4 !Minimize congestion costs of each incremental unit;
SUBJECT TO
   2)  - AB2 -  AB3 -  AB4 +   AB =  0    !Definition of AB
   3)  - AC2 -  AC3 -  AC4 +   AC =  0
   4)  - BC2 -  BC3 -  BC4 +   BC =  0   !     etc.
   5)  - BD2 -  BD3 -  BD4 +   BD =  0
   6)  - CD2 -  CD3 -  CD4 +   CD =  0
   7)    AB +  AC  =  6                    !Flow out of A
   8)    AB -  BC -  BD  =  0            !Flow through B
   9)    AC +  BC -  CD  =  0            !Flow through C
  10)    BD +  CD =   6                    !Flow into D
  11)    AB2 <=   2                     !Definition of the steps in
  12)    AB3 <=   1                            !supply cost schedule 
  13)    AB4 <=   1
  14)    AC2 <=   2
  15)    AC3 <=   1
  16)    AC4 <=   1
  17)    BC2 <=   2
  18)    BC3 <=   1
  19)    BC4 <=   1
  20)    BD2 <=   2
  21)    BD3 <=   1
  22)    BD4 <=   1
  23)    CD2 <=   2
  24)    CD3 <=   1
  25)    CD4 <=   1
END


