Its not left out as it is already in the TinyMud sectionSome use the term MU to refer to TinyMUD MUCK MUSH MUSE MUX and their kin others simply allow the term MUD to apply universally  The problem with the other sections is that after defining the term as a referring to Tinys you then attempt to use MU as a universal term  MU is well known to have two meanings depending on who is using it all muds or only muds from the tiny family  The page uses MUD as the universal term not MU