Man, this is heavy linux/unix commandline fun:
which which
locate locate
man man
help help
info info
whatis whatis
echo echo
touch touch
yes yes
whereis whereis
All of them work without error (unless the programm is not installed or does not work of course)
With nice and time you can even go further:
nice nice
nice nice nice
nice nice nice nice
nice nice nice nice nice
...
time time
time time time
time time time time
time time time time time
...
time nice time nice
time nice time nice time nice
time nice time nice time nice time nice
...
The time-chains work if you ignore the fact that the last time of each chain returns with an error code (because no command is given for that one).
Enough fun and laughter, now back to work.