The forward process makes use of the information contained in the hypothesis A. The backward process tries to find a chain of statements leading to the fact that the conclusion B is true. With the backward process, you start with the statement B that you are trying to conclude is true. By asking and answering key questions, you derive a sequence of new statements with the property that if the sequence of new statements is true, then B is true. The backward process continues until you obtain the statement A or until you can no longer ask and/or answer the key question. With t.
