title: Typing method of a abstract class with an interface
body: <p>Consider this trivial example:</p>
  <pre><code>abstract class Foo {
  
    public abstract functionAdd(number1, number2, number3): number
  
    public abstract functionMultiply(number1, number2, number3): number
  }
  
  interface Numbers {
    number1: number
    number2: number
    number3: number
  }
  </code></pre>
  <p>How can I use the interface <code>Numbers</code> to describe parameters of both methods? Perhaps there's other - more idiomatic - way of defining abstract methods?</p>