dialogue: Addis: Could I have my bill, please?
  Ingelbert: Certainly, sir.
  Addis: I'm afraid there's been a mistake.
  Ingelbert: I'm sorry, sir. What seems to be the trouble?
  Addis: I believe you have charged me twice for the same thing. Look, the figure of 6. 5 dollar appears here, then again here.
  Ingelbert: I'll just go and check it for you, sir.
summary: Addis finds a mistake on the bill, and Ingelbert will check it.