<<< native
[ ESuper
    (ENumber "2")
    (ESuper (ENumber "3") (ESuper (ENumber "4") (ENumber "5")))
, ESymbol Rel "="
, ESuper
    (ENumber "2")
    (ESuper
       (ENumber "3")
       (ESuper
          (ENumber "4") (ESuper (ENumber "5") (EPhantom (ENumber "6")))))
]
>>> eqn
2 sup {3 sup {4 sup 5}} = 2 sup {3 sup {4 sup {5 sup {hphantom 6}}}}