Constraints (2) and (3) together ensure that if a product that has lower COI is assigned to class c and products
with higher COI assigned to class c0 then c is located nearer to the I/O point than the c0. Constraint (4) enforces
that a storage location can be assigned to, at the most, one class. Constraints (5) ensure that each product
is assigned to one and only one class. Constraint (6) ensures that there is adequate storage space to hold
the products in a class in each planning period. Constraints (7) and (8) impose binary restrictions on decision
variables.