theorem
  S is (R6) (R8) implies (a")" <<>> a
  proof
    assume
A1: S is (R6) (R8);
    take a""*1.S;
    thus a""*1.S =*=> a"" by A1,Th2;
    thus a"" * 1.S =*=> a by A1,Th2;
  end;
