I.   The derivation from the lesson.

        Derive P from

               1.   P v Q           Premise
               2.   Q -> R          Premise
               3.   S & ~R          Premise
               4.   ~R              3, Simp.
               5.   ~Q              2, 4, MT
               6.   P               1, 5, DS

      II.   More derivations:

           A.   Derive Q v S from

               1.   P -> (Q v S)            Premise
               2.   ~Q -> P                 Premise
               3.   Q -> R                  Premise
               4.    ~R v T                 Premise
               5.   ~T                      Premise
               6.   ~R                      4, 5, DS
               7.   ~Q                      3, 6, MT
               8.   P                       2, 7, MP
               9.   Q v S                   1, 8, MP

           B.   Derive Q v S from

               1.   P v (T v R)             Premise
               2.   U -> ~P                 Premise
               3.   (T -> Q) & (R -> S)     Premise
               4.   W & (U & V)             Premise
               5.   U & V                   4, Simp.
               6.   U                       5, Simp.
               7.   ~P                      2, 6, MP
               8.   T v R                   1, 7, DS
               9.   Q v S                   3, 8, CD