abstract class A { }
class A1 : A { }
class A2 : A { }
class A3 : A { }

class C
{
  public C(A1 a) { }
  public C(A2 a) { }
}

class X<T> where T: new(A)
{
  public static T Make1() {
    return new T(default(A3));
  }

  public static T Make2<Y>(Y a) where Y : A {
    return new T(a);
  }

  public static T Make3(A a) {
    return new T(a);
  }
}

class P
{
  static void Main() {
    var x1 = X<C>.Make1();
    var x21 = X<C>.Make2(default(A1));
    var x22 = X<C>.Make2(default(A3));
    var x31 = X<C>.Make3(default(A2));
    var x32 = X<C>.Make3(default(A3));
  }
}