I think the initial analogy of discounts is flawed. Its more like Let X be "It is okay for me (Costco owner) to require customers use CostCo credit cards only"

I think the initial analogy of discounts is flawed. Its more like Let X be "It is okay for me (Costco owner) to require customers use CostCo credit cards only" Let not X be "It is okay for me to use my non-Safeway credit card at Safeway"