It's been 20 years since someone showed up at my house and slept on the sofa for a while but in that period visited Sainsbury's and discovered that their implementation of "Buy one get one free" was to remove the price of one object from the total, and the implementation of "Reduced price" was to charge the full price and then remove a chunk and the combination was buy two objects, have both reduced in price, and then deduct the full price of one object
