title: Most flexibilities rule engine for .NET
body: <p>My upcoming project is relate to sales system, so one of the main requirement is "user can modify promotion by themselves". Promotions is vary, they give me some of them.</p>
  
  <ol>
  <li>Buy 1 get 1 free, Buy 2 get 3.</li>
  <li>One for 30%, two for 50%, three for 80%</li>
  <li>Buy product A will discount 30% for product B</li>
  <li>20% off for more than 20$ per transaction</li>
  </ol>
  
  <p>I know a little of rule engine, please suggest me a book to learn it too.</p>