<<< native
[ EArray
    [ AlignCenter ]
    [ [ [ EGrouped
            [ EIdentifier "x"
            , ESymbol Bin "+"
            , EDelimited
                "("
                ")"
                [ Right (EFraction NormalFrac (ENumber "2") (ENumber "3")) ]
            ]
        ]
      ]
    , [ [ EDelimited
            ""
            ")"
            [ Right (EIdentifier "x")
            , Right (ESymbol Bin "+")
            , Right (EOver False (ESymbol Open "(") (ESymbol Bin "-"))
            , Right (EFraction NormalFrac (ENumber "2") (ENumber "3"))
            ]
        ]
      ]
    ]
]
>>> eqn
matrix{
ccol{ {x + left ( 2 over 3 right )} above {left "" x + ( to - 2 over 3 right )} }
}