grammar = {
  "<S>": ["or", "<Statement>", "<Command>"],
  "<Statement>": ["seq", "<NP>", "<VP>", "<NP>"],
  "<command>": ["seq", "<VP>", "<NP>"],
  "<NP>": ["seq", "<optArt>", "<optAdjs>", "<Noun>"],
  "<optArt>": ["opt", "<Art>"],
  "<Art>": ["or", "the", "a", "an"],
  "<optAdjs>": ["opt", "<Adjs>"],
  "<Adjs>": ["seq", "<Adj>", "<optAdjs>"],
  "<Adj>": ["or", "big", "hairy", "blue", "fat", "orange"],
  "<Noun>": ["or", "cat", "dog", "man", "woman"] }
# everything to be with verbs has been ignored