...

         -- Which Prefix Op?
         case Prefix is
            
            ---------------------------------------------------------
            -- Quit...
            when 'Q' =>
               
               -- .. Quit how?
               case O is
                  
                  -- ... with a 'Yes' Verdict:
                  when 'Y' =>
                     Verdict := Yes;
                     
                  -- ... with a 'No' Verdict:
                  when 'N' =>
                     Verdict := No;
                     
                  -- ... with a 'Mu' Verdict: (permitted, but discouraged)
                  when 'M' =>
                     IP_Next := IP; -- Force a 'Mu' Termination
                     
                  -- ... with Debug Trace, and a 'Mu' Verdict:
                  when 'D' =>
                     Print_Trace;
                     IP_Next := IP; -- Force a 'Mu' Termination
                     
                     -- ... with an explicit Tape-triggered fatal EGGOG!
                     -- The 'QE' curtain call is intended strictly to signal
                     -- catastrophic (e.g. iron) failure from within a Tape
                     -- program ('cosmic ray' scenario) where a ~hardwired
                     -- mechanism~ of any kind appears to have done something
                     -- unexpected; or to abort on a failed test of the RNG;
                     -- or similar hard-stop scenarios, where either physical
                     -- iron, or basic FFA routine must be said to have failed,
                     -- and the continued use of the system itself - dangerous.
                     -- The use of 'QE' for any other purpose is discouraged;
                     -- please do not use it to indicate failed decryption etc.
                  when 'E' =>
                     Zap; -- Jettison all resettable state!
                     -- Hard-stop with this eggog:
                     E("Tape-signalled CATASTROPHIC ERROR! " &
                         "Your iron and/or your build of Peh, " &
                         "may be defective! Please consult " & 
                         "the author of this Tape.");
                     
                     -- ... Unknown (Eggog):
                  when others =>
                     Undefined_Prefix_Op;
                     
               end case;