How do I form an 'undo' button in GUI?

Hi, I want to add a push button to undo the last application in my interface. The interface has 5 different applications

The user first open a file as:

handles.file=mywork

Then on every application

handles.lastapplication="..." is used

How can I form an undo function to get the last results before the last application. Is it possible?

I worry about that because every time on every application, "handles.lastapplication" is used. To get the last handle before the last application seems complicated

[Mahdi]

I'm not too sure if there is an undo button, but a way that you can work around it is to store the results from the previous application in a matrix, and add the new application in the next row. That way, you can have a button which lets you redo the whole calculation for the previous value.