That's funny, the example you gave sort of happened during the argument. I would painstakingly establish A. Then I would do something like A => B. Then I would

That's funny, the example you gave sort of happened during the argument. I would painstakingly establish A. Then I would do something like A => B. Then I would remind my opponent that we'd established A, whence B followed. At that point, the opponent would deny that he'd agreed on A, and we're back to square on... very frustrating!