a={}x={}for i in io.read"*a":gmatch"%a+"do a[i]=a[i]~=i and i end
for i,v in next,a do y=v and table.insert(x,v)end
table.sort(x)for i,v in next,x do io.write(v.." ")end
Note that non-ascii characters in the above source code will be escaped (such as \x9f).