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object TypeConstraints{
  // Define some hierarchy
  trait Pet
  class Dog(name:String) extends Pet
  object Dog{
    def apply(name:String):Dog = new Dog(name)
  }
  case class Alsatian(name:String) extends Dog(name)
  case class Cat(name:String) extends Pet

  // Define methods with constraints
  def sameTypeWrong[T <: Pet](a:T, b:T):Boolean = true
  def sameTypeCorrect[T <: Pet, U](a:T, b:U)(implicit ev: T =:= U):Boolean = true
  def subTypeWrong[T <: U, U](a:T, b:U):Boolean = true
  def subTypeCorrect[T <: Pet, U](a:T, b:U)(implicit ev: T <:< U):Boolean = true

  // Try them, to check whether they compile
  sameTypeWrong(Cat("a"), Dog("b"))
  // Does not compile: sameTypeCorrect(Cat("a"),new Dog("b"))
  sameTypeCorrect(Cat("a"),Cat("b"))
  subTypeWrong(Cat("a"), Dog("a"))
  // Does not compile: subTypeCorrect(Cat("a"),Dog("b"))
  subTypeCorrect(Alsatian("a"), Dog("a"))
}