<<< native
[ EDelimited
    "|"
    "|"
    [ Right
        (EArray
           [ AlignCenter ]
           [ [ [ EIdentifier "U" ] ] , [ [ EIdentifier "V" ] ] ])
    ]
, ESymbol Rel "="
, EDelimited
    "\8214"
    "\8214"
    [ Right
        (EArray
           [ AlignCenter ]
           [ [ [ EIdentifier "U" ] ] , [ [ EIdentifier "V" ] ] ])
    ]
]
>>> eqn
left | matrix{
ccol{ U above V }
} right | = left ‖ matrix{
ccol{ U above V }
} right ‖