bothGrandfathersNoPairs.scala

def bothGrandfathersNoFlatMapNoPairMatch(p: Person): Maybe[(Person, Person)] =
  p.mother match {
    case Just(m) =>
      p.father match {
        case Just(f) =>
          m.father match {
            case Just(fm) =>
              f.father match {
                case Just(ff) => Just((fm, ff))
                case _ => MaybeNot
              }
            case MaybeNot => MaybeNot
          }
        case MaybeNot => MaybeNot
      }
    case MaybeNot => MaybeNot
  }

assertBothGrandfathers(bothGrandfathersFlatMap, bothGrandfathersNoFlatMapNoPairMatch)