The blame should be put squarely on the shoulders of tophatter.com. They know the quality of what is being sold and choose to look the other way for the sake of making commission and sales fees on these imitation goods. In my estimation and also the interpretation of the law this is outright FRAUD.
Inverse operations are opposite operations that undo each other. Addition and subtraction are inverse operations. Multiplication and division are inverse operations.
The simplest form of redo is flip-undo, in which using undo after undoing redoes the undone action. In this case, the program flips back and forth between two states when the undo button is pressed. In a more typical redo model, there are separate undo and redo buttons. The redo can be used for each undo action performed.