enter command (? for help): b msg0
===[ msg0 ]===
enter command (? for help): b msg1
===[ msg1 ]===
     msg0
enter command (? for help): a msg2
     msg1
===[ msg2 ]===
     msg0
enter command (? for help): a msg3
     msg2
===[ msg3 ]===
     msg0
enter command (? for help): b msg4
     msg2
===[ msg4 ]===
     msg3
enter command (? for help): a msg5
     msg4
===[ msg5 ]===
     msg3
enter command (? for help): b msg6
     msg4
===[ msg6 ]===
     msg5
enter command (? for help): a msg7
     msg6
===[ msg7 ]===
     msg5
enter command (? for help): d
msg7
msg5
msg3
msg0
msg1
msg2
msg4
msg6
enter command (? for help): a msg8
     msg7
===[ msg8 ]===
     msg5
enter command (? for help): a msg9
     msg8
===[ msg9 ]===
     msg5
enter command (? for help): a msg10
     msg9
===[ msg10 ]===
     msg5
enter command (? for help): a msg11
     msg10
===[ msg11 ]===
     msg5
enter command (? for help): b msg12
     msg10
===[ msg12 ]===
     msg11
enter command (? for help): b msg13
     msg10
===[ msg13 ]===
     msg12
enter command (? for help): b msg14
     msg10
===[ msg14 ]===
     msg13
enter command (? for help): b msg15
     msg10
===[ msg15 ]===
     msg14
enter command (? for help): q
quit