User blog comment:Hyp cos/Taranovsky has updated his ordinal notation page/@comment-29014792-20160910112131/@comment-11227630-20160911035907

Now updated. {1{1(2{2+}2)+2}2(2{2+}2)+2} is enough for SOA.

Also, since (2{2+}2) is a dropper, the plus sign is a separator, (2{2+}2)+ will be a lower-leveled separator than the plus sign. It's just an arbitrary choice that D({1(2{2+}2)+2}) = {1}, i.e. the comma.