<<< native
[ ESubsup (ESymbol Op "\8747") (ENumber "0") (ENumber "1")
, ESymbol Bin "+"
, ESubsup
    (EFraction NormalFrac (EIdentifier "x") (EIdentifier "y"))
    (ENumber "0")
    (EIdentifier "a")
, ESymbol Bin "+"
, ESubsup
    (EFraction NormalFrac (EIdentifier "x") (EIdentifier "y"))
    (ENumber "0")
    (ENumber "1")
, ESymbol Bin "+"
, ESubsup (ESymbol Op "\8747") (ENumber "0") (EIdentifier "a")
]
>>> tex
\int_{0}^{1} + \frac{x}{y}_{0}^{a} + \frac{x}{y}_{0}^{1} + \int_{0}^{a}