content: import React from 'react'
  import Topic from '../Topic'
  
  import { Route,
           Link } from 'react-router-dom'
  
  const Topics = ({ match }) => (
    <div>
      <h2>Topics</h2>
      <ul>
        <li>
          <Link to={`${match.url}/rendering`}>
            Rendering with React
          </Link>
        </li>
        <li>
          <Link to={`${match.url}/components`}>
            components
          </Link>
        </li>
        <li>
          <Link to={`${match.url}/props-v-state`}>
            Props v. State
          </Link>
        </li>
      </ul>
  
      <Route path={`${match.url}/:topicId`} component={Topic} />
      <Route exact path={match.url}
                   render={() => (<h3>Please select a topic.</h3>)} />
  
    </div>
  )
  
  export default Topics