<<< native
[ EArray
    [ AlignCenter , AlignCenter , AlignCenter ]
    [ [ [ EIdentifier "H" ]
      , [ ESymbol Accent "\8594" ]
      , [ EIdentifier "G" ]
      ]
    , [ [ ESymbol Rel "\8595" ]
      , [ ESpace (3 % 1) ]
      , [ ESymbol Rel "\8595" ]
      ]
    , [ [ EIdentifier "K" ]
      , [ ESymbol Accent "\8594" ]
      , [ EIdentifier "L" ]
      ]
    ]
]
>>> tex
\begin{matrix}
H & \rightarrow & G \\
 \downarrow & \mspace{54mu} & \downarrow \\
K & \rightarrow & L
\end{matrix}