MonoidAndSemigroupDefinitions.scala

  // eg union of non empty sets
  trait MySemigroup[A] {
    // must be associative
    def combine(a1: A, a2: A): A
  }
  
  // eg union of sets, where the empty set is the identity element
  trait MyMonoid[A] extends MySemigroup[A] {
    // is an identity element
    def empty: A 
  }