$ scala -Xprint:typer -e "implicit def f[A, B <: A]: A => B = x => x"
[[syntax trees at end of                     typer]] // scalacmd1608811321047988530.scala
package <empty> {
  object Main extends scala.AnyRef {
    def <init>(): Main.type = {
      Main.super.<init>();
      ()
    };
    def main(args: Array[String]): Unit = {
      final class $anon extends scala.AnyRef {
        def <init>(): <$anon: AnyRef> = {
          $anon.super.<init>();
          ()
        };
        implicit private def f[A, B <: A]: A => B = ((x: A) => $anon.this.f[A, Nothing].apply(x))
      };
      {
        new $anon();
        ()
      }
    }
  }
}