问Scala隐式转换问题

EN

trait A {
  def send(s: String): String = {
    println(s)
    s
  }
}

object X {
  implicit def toB(a: A): B = new B(a)

  class B(a: A) {
    def <<(s: String): String = a send s
  }
}

object Y {
  implicit def toB(a: A): B = new B(a)

  class B(a: A) {
  }
}

object Test extends App {
  import X._
  import Y._
  val a: A = new A {}
  a << "Test"
}

error: value << is not a member of A
a << "Test"