For each of the following, either construct a formal proof of validity or prove invalidity by means of the STTT. In each case, use the notation in parentheses.

Their chief would leave the country if she feared capture, and she would not leave the country unless she feared capture. If she feared capture and left the country, then the enemy’s espionage network would be demoralized and powerless to harm us. If she did not fear capture and remained in the country, it would mean that she was ignorant of our own agents’ work. If she is really ignorant of our agents’ work, then our agents can consolidate their positions within the enemy’s organization; and if our agents can consolidate their positions there, they will render the enemy’s espionage network powerless to harm us. Therefore the enemy’s espionage network will be powerless to harm us. ( L, F, D, P, I, C )