<<< native
[ EFraction
    NormalFrac
    (EFraction
       NormalFrac
       (EOver False (EIdentifier "a") (EPhantom (EText TextNormal "!")))
       (EIdentifier "b"))
    (EFraction NormalFrac (EIdentifier "c") (EIdentifier "d"))
, ESymbol Rel "="
, EFraction
    NormalFrac
    (EFraction NormalFrac (EIdentifier "a") (EIdentifier "b"))
    (EFraction
       NormalFrac
       (EIdentifier "c")
       (EUnder False (EIdentifier "d") (EPhantom (EText TextNormal "!"))))
]
>>> eqn
{{a to {hphantom {roman "!"}}} over b} over {c over d} = {a over b} over {c over {d from {hphantom {roman "!"}}}}