From http://lua-users.org/lists/lua-l/2018-03/msg00155.html http://lua-users.org/lists/lua-l/2018-03/msg00155.html. Looks like this was in the first pre-alpha r

From http://lua-users.org/lists/lua-l/2018-03/msg00155.html http://lua-users.org/lists/lua-l/2018-03/msg00155.html. Looks like this was in the first pre-alpha release of 5.4 but removed shortly afterwards: > t[i]=undef is a special syntax form that means "remove the key 'i' from table 't'". You can only use 'undef' in three specific forms: t[i] = undef -- remove a key from a table t[i] == undef -- test whether a table has a key t[i] ~= undef -- test whether a table has a key