title: Subtour elimination constraints of a symmetric Travelling Salesman in IBM Cplex
body: <p>There is a sample code for travelling salesman problem in IBM Cplex. It defined the subtour elimination constraint as this:</p>
  
  <pre><code>   forall (s in subtours)
     sum (i in Cities : s.subtour[i] != 0)
        x[&lt;minl(i, s.subtour[i]), maxl(i, s.subtour[i])&gt;]
         &lt;= s.size-1;
  </code></pre>
  
  <p>Can someone help me with the equivalent mathematical formulation of this code lines?</p>