<<< native
[ EFraction
    NormalFrac
    (EGrouped
       [ EPhantom (EIdentifier "a")
       , ENumber "12"
       , EPhantom (EIdentifier "a")
       ])
    (ENumber "13")
, ESymbol Rel "="
, EFraction
    NormalFrac
    (ENumber "12")
    (EGrouped
       [ EPhantom (EIdentifier "a")
       , ENumber "13"
       , EPhantom (EIdentifier "a")
       ])
]
>>> tex
\frac{\phantom{a}12\phantom{a}}{13} = \frac{12}{\phantom{a}13\phantom{a}}