text: from ..dyck import Grammar
  from ..grammar_utils import *
  
  g1 = Grammar([
      r('S <- W', [(x, y)]),
      O('W', {(a, b, c)}),
      O('W <- W', {(x, y), (a, b, c)}),
      O('W <- W, W', {(x, y), (z, w)}),
  ])
  
  