Lean

language: "lean"

-- a b c       ->      -- a b ¦
-- d   ¦               -- c d ¦
x x x x x              x x x x x
/- a b c               /- a b ¦
   d   ¦                  c d ¦
-/     ¦               -/     ¦
x x x x x              x x x x x