title: Greedy algorithm - Criteria for a coin system to be canonical
body: <p>Given a coin system, what are the conditions that can be used to figure out whether the coin system is canonical. I did read a few papers but nothing solid came off from them.</p>
  <p>I know that greedy algorithm works only for canonical coin systems. I am trying to figure out if the coins ={1, 2, 3, 6} is a canonical coin system. Can I know what is the criteria used to decide this?</p>