title: Cannot convert value of type 'String' to expected argument type 'String.Element' (aka 'Character')
body: <p>I am trying to solve a challenge but i have a problem in a part</p>
  
  <pre><code>func inArray(_ a1: [String], _ a2: [String]) -&gt; [String] {
      var result: [String] = []
      outer: for i in 0..&lt;a1.count {
          for j in 0..&lt;a2.count {
              if a2[i].contains(a1[j]) {
                  result.append(a1[j])
                  continue outer
              }
          }
      }
      return result.sorted(by: &gt;)  
  }
  </code></pre>
  
  <p>but appear a error in this line </p>
  
  <pre><code>if a2[i].contains(a1[j]) {
  </code></pre>
  
  <p>the error is:</p>
  
  <pre><code>Cannot convert value of type 'String' to expected argument type 'String.Element' (aka 'Character')
  </code></pre>