<<< native
[ ESubsup (EIdentifier "L") (EIdentifier "x") (ENumber "2")
, ESymbol Rel "="
, ESubsup
    (EIdentifier "L")
    (ESub (EIdentifier "x") (EPhantom (EIdentifier "z")))
    (ESuper (ENumber "2") (EPhantom (EIdentifier "z")))
]
>>> tex
L_{x}^{2} = L_{x_{\phantom{z}}}^{2^{\phantom{z}}}